Since when are the dunmer not citizens who don't have to pay rent or taxes, can i have a source?
http://www.uesp.net/wiki/Skyrim:Decree_of_Monument
The second paragraph refers to the terms under which the Dunmer accepted Skyrim's hospitality. "Untithed" means they do not pay taxes; "self-governing" and "with no compensation to Skyrim" speak for themselves.
Also Ulfric should be telling his citizens not to treat the dunmer as bad as they do, and free winter actually does start to help them out, the only reason it isn't shown is because that would be a pain for the developers to completely change a whole city.
Since the only part that would be affected would be the Grey Quarter (as there is no indication AFAIK that they will be given other housing, and none is available anyway), I think it would be easy enough to show changes there at some point. We get a damaged Whiterun, Solitude, etc. after other CW events, I don't see how it would be any more complicated to show the same level of change for the better in one small area of Windhelm.
And if we are going to chalk the lack of actual improvement up to game mechanics or limitations, then there plenty of things that Ulfric does or doesn't do for what are probably the same reasons that lead to derogatory comments about him, so IMO fair's fair.

In reality the only thing Brunwulf does that is any different AT ALL is talk about having meetings to discuss plans to decide what, if anything, he will do with the extra money the city will have now that the war is over.
But Ulfric himself cares nothing about anyone who lives in Skyrim who isn't a Nord. He sends his Stormcloak soldiers if a Nord caravan gets raided but not at all when an Imperial Caravan or a Breton caravan or a Khajiit caravan gets raided.
The only person I have ever heard make this claim is Brunwulf. I have done his quest a couple of times, and I always get sent to kill the bandits at Uttering Hills Cave. Apparently they are the ones attacking all the non-Nord caravans. Funny but I've also been paid to clear out the same bandits after Ulfric had his steward issue a bounty on them. So....
Ulfric turns a blind eye to racism in his city as well. Even if he himself is too busy, he has a steward that can take care of those problems.
Whereas the Jarls of every other city take personal offense if one of their citizens - or heaven forbid, their own guards, employees of the hold - makes derogatory statements to you or constantly refers to your non-Nord race in a negative fashion. Except for the fact that they totally don't.
And where did you get that the Dunmer don't pay taxes or anything? Besides, Ulfric would NEVER evict a Nord for an elf. The slum aspect is not because of the Dark Elves. It's because the Nords of Windhelm made it into a slum by keeping them inside that area and straying from that area.
See the link above. And again, the events that caused the mass of Dunmer to flee to Skyrim took place ALMOST TWO HUNDRED YEARS AGO. They were given that part of the city, tax free, rent free, to live in as a self-governing people, long before Ulfric was born, before even his father was born, and he had nothing whatsoever to do with it or how and why they ended up there. By continuing to allow them to live there as they do he is upholding the agreement made between the Dunmer and his forefathers, assuming his family was even in charge of the place at the time. By continuing to maintain their status as a "separate people" (in a political sense) by not paying taxes or being in any other way obligated to the city, hold, or province in which they live, the Dunmer are also upholding that agreement, except they are the complaining about the fact that Ulfric is doing the exact same thing.
And yes, unless you want to believe that Windhelm just happened to have an entire quarter of its buildings sitting unoccupied when the Dunmer arrived, then the people who lived there must have been evicted to make room for them, whether they were Nord or not. Since we do not know what condition it was in when the Dunmer took it over, claiming they were given a slum is an assumption based on bias and not on fact. Even if it was a slum, they've had ample time to turn it into something else, as I've said before - they are not paying rent, not paying taxes, and many of them have what appear to be successful businesses, clearly they are not putting any of their profits into improving the property that they already own free and clear and for which they alone are ultimately responsible.