I remember old arguments back in the day how it "wouldn't make sense" if non-Nords (especially elves) were in the Stormcloaks, which I never fully believed then and even looking more into Elder Scrolls lore, I don't believe now.
So to that, I ask you, what general context can you think of of a non-Nord siding with the Stormcloaks? My case for the dark elves:
While Dunmer in Skyrim feel "safer" under the Empire due to Nord's prejudice and blaming Ulfric Stormcloak for allowing it to continue in Windhelm to the point where they accuse him of being a bigot unlike his father, the Dunmer in Solstheim and mainland Morrowind (as stated by Adril Arano during the quest Served Cold... more on that quest later) are the complete opposite as they HATE the Empire like Nord Stormcloaks do, especially after the events of Oblivion when the Empire pulled out to defend Cyrodiil from Dagon. Worse yet, House Hlaalu, who have been loyal to the Empire, have lost their power soon after with growing power to other Houses like House Redoran and Telvanni (who are both nationalistic in differing ways, hell, the latter I'd argue are FAR more racist than the Cloaks). Granted, I don't see Redoran and Telvanni liking the Stormcloaks either, but still...
And we get to Served Cold from the Dragonborn DLC (which sadly makes no mention of the Skyrim Civil War... come on, you can't tell me the mainland Dunmer don't know that is going on), which involves remnants of House Hlaalu and Morag Tong plotting to kill Lleril Morvayn and knowing House Hlaalu's long history with the Empire and the fact that there is no option to side with them and assist in assassinating the Second Councilor, just doesn't feel right to do as an Imperial aligned Dragonborn. A neutral DB? Sure, as that could be a third party relaying a message acknowledging it's a dirty way of politics. A Stormcloak DB? Sure, as that helps purge what remains of the Empire's influence out of Morrowind (at least in Solstheim).
That's my choice. Yours?