I think there are definitely some other mages that are quite strong on Dominion as well, but they're not the typical SR mages that dominate. I'm thinking about champions like Leblanc, Kassadin, and Karthus (OK he can do well on SR too, but you have to be really good with him). Whereas some of the mages that dominate SR don't do as well on Dominion (thinking Annie, Malhazar, Brand, etc). And you guys mentioned Ryze, but he's more of a tanky AP carry in my eyes. Either way, I think he's definitely viable on SR.
Then there's poppy, who could be classified as a mage.
EDIT: Whoops, obviously you don't build AP on Ryze, but for some reason I still call him AP. I think in general I use 'AP' and 'mage' interchangably, even though they're not. Tanky magic DPS is what Ryze is, not tanky AP dps