My best friend has been in a wheelchair since age 5, and there's not a single disabled bone in his body; he simply doesn't walk. However, he has degrees in both automotive repair and occupational therapy. IMO, not being able to use his legs makes him better at both. He can (I've seen him do this) more easily get into places other mechanics can't, and regarding occupational therapy (he specializes in the recently "disabled"), he knows exactly what they are going through.
Disability is a state of mind, nothing more.
As far as EMS goes, well, why not? Suppose he tries it and the practical aspects get the better of him. What says he can't do something like dispatch?