I don't know the answer, but I'm bumping this up so hopefully someone who does know sees it.
In general, they try to place handicapped rooms in all areas and all floor levels (if they have elevators, not at places that don't).
If you don't get an answer here, you can call WDW Resort Special Reservations:
(407) 939-7807
(407) 939-7670 [TTY]