I don't believe Rubiss is in any other games, but the fourth one introduces a new god-like figure, Master Dragon. He rules the cloud-bound kingdom of Zenithia, and watches over the world from there. During the course of the game, he revives the heroes when they die, and carries them out of Necrosaro's hideout at the end. I understand that he also shows up in the next two games, although I haven't played them. (Here's hoping they'll get DS releases.) From what I've heard, you have to rescue him in at least one of them, so I guess he's no more omnipotent than Rubiss.
I've played but never finished DQ7, but that one has a significant role for God Himself, who's presented as the stereotypical Bearded Guy in the Sky. The Demon Lord of the game disguises himself as the big guy, and I think there's even a bonus dungeon where you can fight God. It's a surprisingly monotheistic game. Even though other gods do appear, they eventually reveal that they're not actually deities. If these games all take place in the same world (which is a doubtful proposition, but kind of fun to think about), maybe Rubiss and Master Dragon are also representatives of God. After all, I can't recall anyone actually worshipping them. Or maybe God is really LESS powerful than them, and just pretends He's all-powerful.