I went last December with a friend who has difficulty standing in line (both the standing and the heat) and we found that when she needed a wheelchair, there was one for her at each line. Since they deny the DAS pass for mobility issues, all rides keep spares to be used when waiting in lines (sh*ty ones, though, not as nice as the ones at the front, lots of broken wheels). It was good enough to push her through lines we were able to stand in, so if he needs, maybe ask a cm to bring you one?
My DH is going to use a scooter for the first time but was scared of some rides have tight turns. I wrote to disney and they told me about each ride having a wheelchair to use. We were planning on switching from the scooter to wheelchair for the rides. I've pushed him in a wheelchair before so that would have been no big deal for me.