Both the Borg and the Founders shared that "bringing order to chaos" mindset but a Borg-Dominion alliance would just be the Dominion's assimilation, but that wouldn't be bad idea either. A Changeling-Borg queen would be terrifying, they clone and assimilate. How would Starfeet stop that?
Gooey nanites spread throughout the galaxy!
You think your liquids are safe..