It has been a long time since I've read Darkover (so ugh if I mess this up), but I believe each tower operates its own way, and the Free Amazons operate outside most rules (but live within the same physical area). There are other natives, but they may not show up in more than a few books each, other than in the background. Not sure if that's good enough for you or not.
UY: Man, I need to not suggest things I haven't read in a while. There is at least one clan of Ninja's that gets a lot of play, there is a couple different families that show up frequently (one of which I suspect plays heavily in the couple books beyond where I've read given the groundwork being laid), there is the big bad guy group. The Shogun himself is barely there, it's more people working around his court. I think there are a couple other clans of ninja's that are recurring. There are also the bounty hunters, but those are probably too loose & every man for himself for you. I don't know if they are different enough cultures--they are all in the samurai culture, but they approach it differently. I should reread those and I might have a better answer.
GC I could have done better on if you'd asked. England (at least in frequent passing), Hetrodynes (and even moreso the Jaegers and Mechanicsburg citizens since the Hetrodynes themselves are down to one person raised outside), Storm King, and Wulfenbach are the big ones who get play.
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UY: Man, I need to not suggest things I haven't read in a while. There is at least one clan of Ninja's that gets a lot of play, there is a couple different families that show up frequently (one of which I suspect plays heavily in the couple books beyond where I've read given the groundwork being laid), there is the big bad guy group. The Shogun himself is barely there, it's more people working around his court. I think there are a couple other clans of ninja's that are recurring. There are also the bounty hunters, but those are probably too loose & every man for himself for you. I don't know if they are different enough cultures--they are all in the samurai culture, but they approach it differently. I should reread those and I might have a better answer.
GC I could have done better on if you'd asked. England (at least in frequent passing), Hetrodynes (and even moreso the Jaegers and Mechanicsburg citizens since the Hetrodynes themselves are down to one person raised outside), Storm King, and Wulfenbach are the big ones who get play.