It is legal. You are not obligated to do this--that is, it is voluntary to set up a non-profit to do this, or for an existing one to add this benefit or service. And it is voluntary for students to apply for the stipends--they do not have to apply for or accept one. Since it is a purely voluntary endeavor, you have the right to ask for whatever information you feel is relevant; someone who does not want to disclose that information does not have to apply for a stipend.