It's possible that it depends on the school. Although I don't have first hand knowledge, when I went through orientation for my grad program last summer, they made the announcement that if anyone has a disability, they need to make sure that the university disabilities office has the paperwork for it, to allow the school to make any modifications necessary for the student. I don't have a diagnosis, because I don't have insurance or $1000 burning a hole in my pocket to pay for it, but I will probably eventually get one. My GRE scores might have turned out better if I would have been able to get modifications-even if it was just to take the test in a room by myself. When I finish school, I will have to take a large licensing exam, that has me really worried, and that will definitely push me closer to getting a diagnosis, but we'll see. Maybe you should look into how the school that you'll be going to views it, if you can.