Here's a thought I had while examining the Outer Gods on Pathfinderwiki. The underlying information I'm aware of might be out of date.
What if Groetus is connected to the Outer Gods and Yog-Sothoth in some way? Perhaps after Yog-Sothoth gets summoned, likely unleashing Rovagug in the ensuing chaos, and all of reality is warped and shattered, Groetus comes in like a janitor and sweeps all the strangeness out of the planes and restarts the pilot light? Or something like that.
Didn't devote much thought to it. Just popped into my head after reading Yog-Sothoth. Enjoy and Discuss I guess?
I don't think that Groetus himself is an Outer God, but I can imagine him playing poker with them on weekends.
Or sharing rented spaces for cult meetings! 8D