MU Dominion is still "The Dominion". The Founders used a bit of trickery to impersonate the deities of the worlds they rule, and convince their populace that their beliefs all refer to the same beings - them. They actually make pretty good "gods", and rule over their worlds in a mostly benevolent fashion. The Vorta act as their mortal spokespeople, and the Jem'Hadar as sort of their angels or paladins.
They sent sleeper agents to the AQ, just like in the RU. When the wormhole finally opened at Terok Nor, the Dominion fully saw what they were dealing with. The agents were "awakened", and given orders to continue shaping matters for later. The Dominion then explosively closed the wormhole.