For some reason I am trying to imagine a horse riding a ATV or a wheelchair and I think no.
You are going to be at least one half of a horse overflow.

If you want to be nice you could say that they can sit in it if made for a larger demon/devil i guess but they will have disadvantage on checks to use the vehicle.
Or give them a devil ride of their own that is basically hellish training wheels they can put on their hooves.