It'd be a ragtag collection of aliens,
Probably the only ones with legitimate cause... :dead
mercenaries,
Who don't give a damn about legitmate causes, freedom, equality or democracy but money. See Union.

smugglers,
Because the *new* government these aliens, mercenaries, thrill seekers and lovers of freedom, equality and democracy bring about will definitely support one's freedom to smuggle. :yuck
thrill seekers,
Yes..yes... it's all a game until their homeworld get's blown up and then it dawns on them, "Damn, this shit is for real!" o_O
and those who simply fight for freedom, equality, and democracy because they believe everyone deserves to have it...
..and because there are so many examples of how well it's worked so far.. See: Old Republic...wait... See: New Republic...wait... See: Galactic Coalition... :ohwell
(like Leia was in the first rebellion).
She was also 18. And a virgin. <--- I just threw that last one in there for no reason.

I don't think Azguards would be the core of the Rebellion...
What? Who better than those who make hating the Empire a religious euphoric experience? :b
I'd say it'd be more general like, aliens are the core of the rebellion.
Which is run, ironically, by their human elite. Or should I say, by their rich human elite. :glance
:grin
Still, your points are well taken.