The buildings are a bit strange for rebels. They seem to be tied to region somehow—perhaps the culture type in descr_regions.txt or descr_strat.txt (they don't have to be the same for a given region). There are rebel subfactions, one per real faction. I don't know how this all works, exactly, but the way to check is to start up a game as the rebels (after editing descr_strat.txt—and keep in mind that if you have more than twenty playable factions, you won't be able to play any after the twentieth, so you can't have all factions playable at once).

-Simetrical