Often with an
ECV, the cast member will ask you (the person using the ECV) if they can walk/transfer/step down (all depending on what is needed to board the ride).
I know there is one ride at Disney where they ask me if I can walk, walk some number of feet and go up or down stairs. I can't do stairs, so they send me another way. It might be in Animal Kingdom.
All of that to tell you, they will know what he has to be able to do. That way, you can evaluate it before he gets in line.