You make vaid points, Big D, but the japanese version makes it pretty clear:

Ultimecia: Your feelings, I shall summon the most powerful of things [from them]! The more strongly you feel, that will be what shall torment you. Fufu.

The implications are that it is their feelings that she is using against them, not simply a GF. Although I agree that Griever is(was) probably a legend from the past, I think it is pretty clear that Ultimecia never actually caught this legendary GF. Instead, she fashioned one based on Squalls image of him.

As for the Square denying the theory in a magasine, it sounds rather suspect, but if it's real, that'd be great.