Josh (Rubix) does indeed say this is the case, though I wish I had the exact question/quote, of course.
EDIT: To be precise, this is what Josh said, and I have not heard any specific reference that they "tend to fall in pairs." That is a more implicit assumption. If you have a clear quote, I'm first in line in wanting to hear it.
I think of it like Allomancy. Sure, there is Pushing and Pulling, which are opposite powers, but you also have tin and pewter, which while they are pairs, they aren't opposites, just complementary. I think this is the case with Aona and Skai. It is perfectly possible that Skai is Unity (or at least a synonym of it).
As for AonDor being of Skai, I don't know about that. It feels right having it linked with Aona, simply based upon the name, but it's hard to know what the Dor is. Possible, I suppose. There's not enough information to really make a detailed judgment.