Well we did decide to get him. Also got more info on him. Turns out his issues stemmed from being buddy sour. It was the owners daughter that got thrown off back in June. We came to the conclusion that he was throwing a fit being taken away from the other horse. So it wasn't from pain or spooking. Not all the details were clear because the daughter wasn't there.
They wanted to sell him because they just didn't have enough time to ride him often enough and not because of the bucking. You could tell that she, the owner, was hesitant of letting him go.
As for the dressage training, the owner wanted to learn how. They felt that even though he wouldn't he wouldn't perform for shows, the training wouldn't hurt for him to learn.
I didn't ride him yet but hope to this weekend, weather permitting. Just going to let him settle for the week and start getting introduced to the herd. His ground manners are really good and he seems like a calm horse.