All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
If a student enrols in this university while sincerely intending to study in it, and then the university compensates him with a commission if other students to register in it because of him, then there is no harm in taking this commission, this is what is religiously called Ji'aalah, a conditional payment, and it is permissible. For Ji'aalah to be permissible, the amount of money [or percentage] should be defined at the beginning.
However, if the student is not actually willing to study in this university, and he just enrolled and paid the tuition fees in order to obtain the commission by inviting other people to enrol in it, then it is not permissible to take this commission as the student pays the fees and it is not sure that he will get other students to enrol in the university. This is nothing but gambling as the student is either subjected to win or lose.
For more benefit, please refer to Fatwa 90248.
Allaah Knows best.