I had just assumed it was the same developer as Sins or Gal Civ 2 as it was a Stardock product
Those two are not even developed by the same teams--Sins was made by Ironclad. Sins was the first title we've published but not developed in-house, though we have a very close relationship with the devs and a hand in the design process (likewise, they have more say in the publishing stuff than most devs who don't self-publish do).
The arrangement with GPG for Demigod is similar. We're taking a hand in the design and providing the ImpulseReactor code, while they likewise get more say in publishing stuff than they did with THQ (for example). It's a much closer relationship than the usual dev-publisher arrangement, but we're still separate companies with our own staff.