Not every DME bus is wheelchair accessible, but many are.
If you are able to let them know ahead of time that you need a wheelchair accessible bus, it's supposed to shorten the wait because they will have one there when you are expected to need it. If they don't know ahead of time, they will get one there for you.
The wheelchair buses are the same as the regular buses, but they have a lift at the back. Be prepared that the lift will take you way up in the air (those buses are pretty high). Once on the bus, the driver unlatches several seats and rolls them toward the front of the bus on a track to make room for the wheelchair.
The getting back to the airport part is more important for them to know you need a wheelchair bus since you are on a time schedule then. The other thing to keep in mind is the time they give you for bus pick up to return to the airport is the time the loaded bus is scheduled to leave the resort, so be there enough ahead of time.