Having done both sides of the Civil War now, I would never have my Orc join up with the Stormcloaks. The miopic xenophobia and outright bigotry just got on my nerves. I can justify it when playing a Nord, but never with any other sort of character. The Stormies will never trust you and never respect you and who the heck wants to live a life like that.
I luv my Orc and he helped to settle the conflict quickly and efficiently and I have to admit, killing Ulfich was and always will be a wondrous thing for me (don't get me wrong, killing Rikke & Tulius are pretty good too when I'm playing a Nord).
I realize that a lot of people have issues with some of the restrictions place on peoples by the Imperials, but, frankly, I just don't see them as that bad. It's not the empire that pursues the religious intolerance and bigotry. There are other groups for that (e.g. Thalmor, Storm Cloaks, et al.).
I just find the whole Stormcloak movement so short sighted. Who is going to support them in the long run. Sure Skyrim is a big place, but it's sparcely populated and almost any army can come in and take over if they have the right numbers and equipment. Humans (and most mer and beast races) have a common enemy and splintering it serves no purpose. Most of the Nords in Skyrim don't even support the Stormies in any case (of course they don't really support the empire either). They just want to live their lives and could give a flyin' fig.
Sorry, just my opinion.