Well, I've been watching the entire game of redguard on Toutube and started thinking (I know, you're shocked) that Morrowind kept its own culture by signing the Armistice, and Hammerfell kept it by kicking Septim's ever-living ass back to Skyrim, but what other cultures have escaped full Imperialization and how? I would think that Summerset, having joined the Empire because Septim had Numidium, maybe managed to keep a good amount even if the national pride was mortally wounded by being subjugated by lowly humans. Black marsh is Black marsh, of course, and if Bruma is any indication Imperializing Nords is like teaching Bears to read. Go ahead and try, but you'll probably just fail and get killed. And Orcs only just joined the Empire, and I believe Orsinium, as a city-state type thing, maintains the ancient warrior culture of the Orcs.
But are there any concrete sources to say how Imperialized each place is? Really so far all I have is the above guesses.