I think it was in Treachery, Faith and the Great River the defective Weyoun mentioned that the Vorta were once apes, and became who they were in reward for saving a Changeling's life. Could that have been true, or something the Founders made up to reinforce themselves as gods? I wouldn't put it past the Founders though, to get some primitive species and engineer them to serve their own ends lol..
I think the whole "primitive ape-like creatures saved a Changeling" is too cutesy to be entirely true, but I think it must be partially based in reality. It's likely the Founders found a humanoid species that was especially subservient and cooperative and genetically modified them to serve their needs. As far as the Founders having to reinforce themselves as gods, their god status seems pretty hardwired into the Vorta and Jem'Hadar. I don't think much reinforcement is necessary.
Well we've seen rebellious Jem'Hadar more than once, and even Weyoun said that their hardwired loyalty to the Founders is "overstated." Even Keevan put his selfish desire to stay alive over the Dominion and Weyoun 7(I think, the one in Faith, Treachery) twisted his loyalty to Odo alone while Weyoun 8 was talked into killing Odo that same episode by Damar.
It was Weyoun 6 that was the defective clone and Weyoun 7 that talked with Damar into concealing the fact that Odo was aboard that roundabout. Anywho, it could be a fairy tale told the Vorta by the Founders. After all the Vorta are the silver tongued negotiators of the Dominion. They can spin a tale like no other, even to their "gods" the Founders.
At first I thought it was just a Founder lie but I've come to wonder why bother? Is uplifting a more powerful reinforcement of their role as gods over a creation from scratch story? Neither way it allows the Founders to claim the spot as the Vortas gods. One reason why this tale exists might be as a tale to show the benevolence of the Founders, that if you help them (in by definition the Dominion) great rewards could be yours.
It's probably something based on the truth but mythologized. The fact that the story includes a Founder being hunted by solids lends it more plausibility. It's very plausible that a Founder was protected by a Vorta, and that initiated a sequence of events that led to the Founder using the Vorta. The rest of the story is no doubt exaggerated.