It originated as a Marvel property, that's all that matters, because Universal owns the rights to those within those families. Once GotG joins The Avengers, that suddenly becomes a Marvel property that is part of that "family", as the legal language designates. The MCU is totally fair game and able to be used by Universal, and thus that counts.
I don't see how this is so hard? Why do people really want a Guardians ride at Epcot this much to search for any loopholes?