Is this Yoga suitable for persons with psychological challenges?

If the Divine were to see and judge human beings the way we do then surely no one will be considered as fit. From the Divine point of view there is no category as unfit but those who have reached a point, whence they are ready to undertake conscious yoga (which is what perhaps you mean by fitness) and those who have not yet reached that point but are getting ready towards that. We can thus look at this as a two-stage process rather than as a yes or no. The first stage in when the Divine is leading us from behind the veil just as a baby in the womb who knows not his mother but is yet fed and protected and cared for by her. When the time comes then the soul enters the second stage of conscious evolution. That is what is called as yoga. It means that the evolution of the soul is now undertaken directly by the Divine who comes to lead the soul no more indirectly through the cover of ignorance but directly as the Master, Guru, Yogi, chosen Deity or Ista Devata, Vibhuti, Rishi or the Avatara Himself. Or else the person gets intimations from within, is led to a book or place or persons through whose contact the veil is torn and the direct leading begins. In other words, the Divine never abandons anyone. If He did then there would be no hope for anyone. Even the strongest of men, even those whose nature is very well prepared are still within the magic fence of ignorance and without the Grace of the Divine Mother they cannot cross over. These are well recognized facts of spiritual life and it is only logical that it be so.

In the Integral yoga, however the issue is little more complex since the aim here is a transformation of nature from the animal–human to a divine humanity.  Even when the soul is ready and some parts of nature are also ready, there are other elements that may not be ready or even resist the pressure of the Divine Shakti towards the intended transformation. But here too the main thing is not the possibilities and difficulties of nature as much as the readiness of the soul to open, receive and submit to the workings of the Divine Mother. The fitness or unfitness is not so much about the ‘negatives’ as much as by certain positives that awaken in nature due to the awakening of the psychic element or the secret soul within. These elements which are actually soul qualities reflected in nature are faith, surrender, will to persevere despite whatever obstacles that may come on the way, endurance since it is a long journey, patience and an unfailing trust and confidence in the Grace. Of course, if there is the central sincerity and a combination of strength and plasticity then it is wonderful. But even if these are lacking in the beginning if one is ready to develop them by a progressive effort and opening to the Grace then that is enough. What is meant by central sincerity is that the will to undertake yoga is not motivated by selfish desires and aims such as ambition to be a yogi or a guru or get miraculous powers and any such things that would only aggrandize the ego-elements. Especially dangerous is an excessive sexual impulse often combined with perversion and an excess of ambition. These are the two main dangers and of course fear which leads to a shrinking inside the comfort zones of the ego-self rather than go through the fire and blaze of yoga.

Yet the most important elements are not defects of nature as the will and capacity to open to the Divine Influence through aspiration or prayer or any other form of contact that the Divine may use to pour His Force upon the sadhaka. Especially helpful is a deep psychic bhakti with an urge to give oneself to the Divine and His work. If that is there from the beginning then it is sufficient to carry us through all the difficulties of nature and the challenges of inner and outer life. But to those who cannot thus open, either because the ego structures are too rigidly resisting or certain strong formations of nature then the journey can become a risky or at least a tumultuous affair. Still if the faith, devotion and surrender are solidly established in nature one can go through these and every other difficulty if the call to yoga is genuine and one is willing to follow it right up to the end, the challenges notwithstanding.

FITNESS FOR YOGA
(below are the words of Sri Aurobindo on the subject)

Nobody is fit for the sadhana—i.e. nobody can do it by his sole capacity. It is a question of preparing oneself to bring in fully the Force not one’s own that can do it with one’s consent and aspiration.

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It is useless to raise the question of fitness. No one is fit—for all human beings are full of faults and incapacities—even the greatest sadhaks are not free. It is a question only of aspiration, of believing in the divine Grace and letting the Divine work in you, not making a refusal.

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It is difficult to say that any particular quality makes one fit or the lack of it unfit. One may have strong sex impulses, doubts, revolts and yet succeed in the end, while another may fail. If one has a fundamental sincerity, a will to go through in spite of all things and a readiness to be guided, that is the best security in the sadhana.

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Fitness for Yoga is a very relative term—the real fitness comes by the soul’s call and the power to open oneself to the Divine. If you have that, you have the fitness, and your past actions cannot stand in the way: the past cannot bind the future. Of course, you have to finish with it, reject it and turn into the new ways—otherwise the past remains the present. But that is the question of the will in you and the soul’s call. If you are faithful to your soul’s call there is no reason why you should not be able to do Yoga. All that you have to do is to keep your aspiration and not lose the inner connection that has been made—then the Mother’s thought and the help will be with you and you will find your way.

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You speak of your possible unfitness, but it is not a question of fitness or unfitness. There is nobody who can go on in his own strength or by right of his fitness to the goal of the sadhana. It is only by the Divine Grace and reliance on the Divine Grace that it can be done. It is in a strength greater than your own that you must put your first and last reliance. If your faith falters you have to call on that to sustain you; if your force is insufficient against the ill-will and opposition that surround you, open yourself to receive that force in its place.

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All can be done by the Divine, the heart and nature purified, the inner consciousness awakened, the veils removed, if one gives oneself to the Divine with trust and confidence—and even if one cannot do so fully at once, yet the more one does so, the more the inner help and guidance comes and the contact and the experience of the Divine grows within. If the questioning mind becomes less active and humility and the will to surrender grow in you, this ought to be perfectly possible. No other strength and tapasya are then needed, but this alone.