Quote Originally Posted by rotten View Post
Or, think of it this way: they're mercenary and they're high nobility. Maybe they performed some sort of transgression at home and were exiled, or they were defeated by a rival tribe and fled, or are simply a collection of non-firstborn sons with a big name and enough money for top equipment, but no actual inheritance.
The idea of a client ruler is to appease a subdued people through them being ruled by one of their own, so it really doesn't make sense for the client ruler to belong to a different ethnicity.

The practical problem is, you'd need an ethnicity for every province, just for client rulers and you'd need to make sure only those can get the trait (and the correct one).