Does this mean you can win a diplomatic victory even if some of your "allies" are at war with each other? This is interesting, because I had a game with the Drengin, Arceans, and I think the Yor left, and I was allied with the Yor and Arceans, and the Drengins were fighting both of them, but my relations with the Drengin were "warm". Which surprised me since I'd been at war with them as well and taken some planets (first planet I took: Drengin homeworld!) before I offered them peace, which they graciously accepted.
I debated giving them some gifts to make an alliance, but Ifigured that wouldn't work for a diplomatic victory since to me it makes sense that no one is fighting to get the win. Instead I declared war on them again, and after taking 3 more planets from them, they realized it was hopeless, gave everything to the Arceans, and the next turn I had a diplomatic victory.