So I was playing around with the game, used the civic Syncretic evolution. Made the subservient species that was the same as the Primary species, same picture and name. The Sub species was considered part of the primary. I give Paradox two thumbs up for getting that right. It turned out I couldn't enslave the sub race, even though the primary race was Authoritarian and xenophobe. Slave guild and syncretic evolution prevent each other. What I would like to see is if you give part of your race subservient, nerve stable, or delicious trait you should be able to enslave them or even purge despite the race being a sub race of yours.