The Dominion, with the hundreds of races belonging to it, was created solely for the Changelings and by the Changelings, so it's only logical that they would have the absolute rule. If they decide to do something, it gets done, otherwise, Jem'Hadar will come for a visit. The administrative link between the Changelings and the membership worlds are the Vorta. However, the contact is not so tight as one might think. Ornithar's words in "The Search, Part One" provide a different picture. According to what he says, the Dominion members can act mostly independently, as long as they follow certain guidelines, of course. However, the Karemma were relatively free to chose with whom they trade, what they trade and how much of it. Additionally, since contact is only established through an unmanned subspace relay station, contact with the Vorta seems to happen rarely anyway.

A different chapter are of course the Jem'Hadar, who basically have no personal freedom at all. Bred for combat, they actually don't know anything else, as it was implanted into their genetic makeup. A growing dissatisfaction among Jem'Hadar is the natural outcome. It's quite possible that large groups of Jem'Hadar will defect as soon as someone else can provide them with their missing enzyme.