I have been on many WDW tours. All are accessible. For some of them a persdon in a wheelchair or
ECV might have to use a different entrance than everybody else, but they will make accommodations.
Another thing. Legally you do
not have to let them know in advance of special needs. However, if you do let them know they will be ready and, for example, will have sufficient transportations for all in wheelchairs and/or ECVs on that particular tour.