Except, like I said, minor races are not part of the UP.
Considering they can trade with you, I'd rethink that statement. As I recall, if you leave the UP, you lose the ability to trade with other races, correct? Therefore, the minor races are clearly a member of the UP, except they don't actually get a vote in it. Probably because they have no
influence, at least as far as I can tell. Heck, one time I actually got a minor race that had his homeplanet literally within 5 parsecs of my Homeworld, and I don't recall my homeworld getting affected by any foreign influence on the planet info tab.
Hmm, the UP doesn't allow trade routes with non-members, either, and you can set up trade routes with minors.
I get the impression that all minors are considered to be subject to the UP, and have been since GC 1.
Best as I can tell, you've got it completely right.