I think it is more likely that Rinoa is a descendant of Ultimecia, rather than Squall, though that would also explain how Ulti came to be in possession of the Griever GF, hidden in Squall's ring. However, I feel that it would be more symbolic if Rinoa was responsible, her becoming a sorceress and all. And Squall gave her the ring.

As for the Zell/Ultimecia similarity thing... I think that's just pure coincidence. But interesting thought...

Uh.. FE... are we playing the same game?