I really am failing to see where this guy is mistreating the horse; His hands and body are really quiet while he is riding, he's not tugging on the horse, but has that constant pressure that is typical for gaited horses...he isn't forcing his nose in, nor is this horse's head really strung up. On the ground, again, very little pressure was needed; the horse looked relaxed in his presence, and I think the horse is trained that when you return, that's his release. He didn't "Back Up" he 'stood up'.
Anyway, to the OP, I would say go and try him out; try him on a looser rein, but don't be surprised if the horse is forward moving, and 'looks' for that pressure. This CAN be fixed with some persistence, and patience, but don't expect him to "not" want to "go" with less pressure right off.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."