theoperation
Hero of Jorvasskr
I'm also unsure of your point about how the Dunmer were always treated badly in Windhelm even when the Empire was in power - which would apparently give Ulfric (and the Stormcloak government) a free pass. As I've said before, he may not have started the policy, but he hasn't lifted a finger to change it in all these years, so he's a party to it. It certainly doesn't seem to bother him enough to care about changing it. When the Empire wins, Brunwulf sets about initiating change, but slowly. Cautiously. Several NPCs (Dunmer and non) have optimistic and grateful things to say about his efforts.
I would have to read up more extensively on Windhelm city history and lore, but do we know for sure how long ago after arriving that the Dunmer were confined to the slums and refused broader opportunities? Rolff makes it sound like the king at the time invited them in in a friendly and sympathetic fashion (which could just be Rolff's own bitter slant), but I haven't seen or heard much about the nature of a timeline of the segregationist policy. Maybe I need to speak with Ambarys more as well, but I'd be curious to find out any sort of tangible date for when everything started to deteriorate.
The argument was that it was Ulfric Stormcloak that started the policy of segregation against the Dunmer, but I argue that it wasn't started with him.
I don't know the date, but I think that it does predate Ulfric's time. Considering that the Dunmer life-span is about 200 years, most of the Dunmer would be considerably older than the Nords. I haven't heard any of them say "It was better before Ulfric", and it seems to me that it's always been like that, as long as they've been around. And considering that before Ulfric was around the Stormcloaks weren't even invented yet, it is reasonably safe to say that Windhelm had racial segregation when Windhelm was under Imperial control.
But considering the Jarls are quite independent, I'm not going to blame the Empire for it, rather Ulfric's predecessors, coupled with tensions between three different but equally proud and stubborn that have been forced to live together.