I think that it is a very personal decision as to whether or not you allow your child to go off to school with “this health issue” as there are a lot of different factors, such as where they are in the recovery process (if they are even in recovery) and if there are support systems in place. Ultimately, the decision is up to the individual family as to what they think is best for the student.
I have been to several shows at the school where my S17 is pursuing a tech degree and i have observed that the performers run the gamut in size and looks, though all are talented. Perhaps you can look at photos of the classes or the shows at various schools and get an idea of what the physical body types of the members are. This might be more telling than just asking because I bet that few schools are going to tell you that they body shame students or don’t accept kids who don’t meet physical norms.