I kinda laughed at your race issues, and how easy they were to solve.
Also, how do imperials don't fit into an all nord group when at the start an Imperial man came to give Ulfric with valuable information without being cast out as malicious or false.
Two days passed before an Imperial man came before Ulfric with valuable information. He said that the man was from the elusive Cult of Fire, a revolutionary movement that wanted to overthrow Ulfric. He said that the Cult has four leaders, all answering to a single ruler. No-one knows where they are based, who they are, or how many they number. The Imperial's body was found on the banks of lake Calenhad the next day, with a fireball symbol carved into his bare, bruised chest.
Also, I point out that Imperials are in fact divided into a whole bunch of sub-races. Colovian and Nibenese. Colovian actually having a great deal in common with Nords. Nibenese are the ones that have the culture that alienates the nords.
Also, in general. Ulfric isn't even the racist one of the stormcloaks. Belyn (Dunmer) even says, "The only way to win the Nord's respect is through hard work." I mean, sure the Dunmer and Argonians are treated like crap, and given the utmost crappy place to live, but he did actually cater for them. There is even a Dunmer who is pretty high up in the ranks. Belyn Hlaalu, who owns Hlaalu farm that is apart of Windhelm. So, if he was truly xenophobic against any race, why would he let him keep that farm?
He also allows non-Nords to live peacefully in Windhelm and own businesses, including Altmer and
Imperials.
The only real problem race, are the Argonians, who are only not allowed in the city (another city does the same, but I can't think of them), but they can live outside it. He does business with the Dragonborn if he is Argonian. But think about it, the Argonians invaded morrowind at the time of the Red eruption. They are enemie (not all of them) of the Dunmer, who currently reside in Windhelm.
Khajitt, that only stays with the khajitt caravans, not the actual Khajitt nation (That we have yet to have seen).
So yeah, I just wanted to stop by, and say this was a lovely RP idea.
Sorry about the long arse story, but there is perfectly good lore to explain everything.