Jurgarik Greycloak
Techno master of Tamriel.
When it comes to the reasons, I think you got one wrong. Just because Nords are the only ones joining does not mean they are racist. The ignore Adrienne likely because they know her father was the advisor to the old Jarl Balgruuf.
Understand that I said most of them are. Sure, there are many exceptions to my Racism Criticism of the Stormcloaks, but more often than not, the amount of Racist Nords out ways that of the Tolerant ones. I didn't mean that they ALL were racist and ignorant, but most of them.
Unless you count Rolff and his buddy as stormcloaks, none of the rebels are truly racist. It is just that Nords seem to be the only one that gets drawn to the rebellion.
Plus, it is not really racism to begin with, but lack of trust in other races until the members prove themselves. The only ones the nords are truly "racist" towards are the Khajiit, and that is because the cat people brought that on themselves.