They're the same game. I think ACW Solitaire might have a few extra land regions out west, and it includes rules for Indian raids which were omitted from Confederate Rebellion. I've read both rulebooks and they really are the same game. My understanding is that the Indian raids didn't add much to the game anyways.
I'm looking forward to trying this game. I managed to get through a few turns one night to familiarize myself with the rules, but haven't gotten to play a full game yet. It looks pretty cool.