Yes, colleges can ask for anything thing they want when it comes to distributing their money. They can ask for divorce decrees, to see support orders, visitation, documentation of support paid and unpaid, copies of orders of protection, police reports, etc.
Your mom can basically say anything, which is why the colleges will not take a request for a non custodial waiver solely from her. The neutral third party does not have a vested interest (where you and your mother do)