Is it permissible for me to supply workers to the contractor in exchange for a commission that I take for myself, knowing that I supervise the contractor, and that the company does not allow the supply of workers except through this contractor, and is it a condition to inform the workers or the contractor that I am taking the commission?

What appears evident is the prohibition of undertaking this work, due to the suspicion of favoritism towards the contractor, given the benefit you would gain. This is if the work is outside official working hours. As for during official hours, the prohibition is beyond question. You should guide the contractor to ways of fulfilling his obligations, as an act of charity and benevolence, without entering into a contract of exchange with him.