Am I allowed to pay for a dorm for the university I deposit for on May 1, and then cancel all of that if I am accepted off a waitlist for a school after May 1?
Allowed to? Yes. Might you lose the deposit? yes.
In your situation, and especially if you view that your chances of getting off the wait list are significant is to delay payment for dorms for as long as possible. The down side of delaying housing decisions is that you may end up with a less desirable room. There really is no harm in asking the question of the housing office rather than college confidential. You can pose the question in a way that simply suggests a delay in choosing housing for personal reasons. They won’t withdraw your admission if you ask. In any case I expect that you’ve already paid some deposit to the college (that most likely goes toward tuition and fees). You will most likely lose that if you don’t matriculate.