I added a lot of new reagionals to the Sabaean unit roster. Works like charm. For reagionals it's easier, cause you can just copy the whole list from another faction with all the hidden resources already set properly. I've added a number of factional units that have the description of being rebellious locals to the reagional lists.
Works like a cursed charm, you mean? If you do not add sprites and stuff for the faction it will cause CTDs like the one you reported when they are used in battle.