Raft guide school is a great way to go. I would add, however, that many outfitters focus primarility on guiding paddle boats. The outfitter I work for, and the area we are in, 90% of trips are paddle boats, so we spend 90% of our time on that. I would suggest trying to find an outfitter the relies heavily on oar boat trips to do your training with, if that is what you are most interested in.
FYI- I don't know firsthand what kind of whitewater skills they have, but I do know that fishing guide outfitters do zero paddle boats, but they still have to cover all of the state training requirements that whitewater guides have to take. You may be stuck learning about fishing holes, but at least up here in the central mountains, you would get fully oar-centric practice and training.
Check out these guys: http://www.flyfishingoutfitters.net/raftschool.htm
Maybe your best bet would be to look for a whitewater company that also does flyfishing. They may have a more whitewater oriented oar training class. Most fishing guides try to avoid all the good stuff!