Well i dont mean Anu was literally a god. But as far as a godly definition goes. He's got some of the key points that you could attribute to our definition of a god.
First being in the universe. Check.
Created the universe. Check.
Effects nothing in a direct way. Check.
Created a group of moronically pious zealots who seem fairly intent on ruining mankind. Check.
That sounds like a definition of god to me.
Well, the only reason he doesn't affect anything in a direct way is because he's dead...
When he was alive all he did was fight the seven-headed dragon, and that was before most of creation existed.
He also didn't exactly create The Universe, though he certainly did have the power to create planes of reality. Yet the only two currently known stable planes of reality (aside from Sanctuary) The Heavens and The Hells only came about as a result of Anu's and the Dragon's deaths. The Heaven's coalesced around and from Anu's corpse. Likewise the Hells spawned from the rotting carcass of the Dragon. They weren't really Creators as we understand godly creators (ie: ones that actively sought to create the world). The Heavens and The Hells were just a byproduct of their demise.
Also, Sanctuary wasn't created by Anu, although one could make the argument that it is because of Anu that Sanctuary could be created. Inarius, an angel, created Sanctuary (albeit with Anu's Eye, aka The Worldstone).
As for Pious Zealots... I'm not sure whom you're referring to. If you mean the angels, again they only came about after Anu had died. They're a byproduct of his death, and embody the virtues of his beliefs. If you meant the Zakurum, those were technically the disciples of a prophet whom experienced a vision of Uldyssian's sacrifice and death.
Now with all that said, I would certainly agree that Anu had God-like Powers, but he's never been worshiped as a God.
What I find more curious than anything else is how powerful the Nephalum appear to be capable of becoming if Uldyssian is any indication. With both the potential for Good and Evil, it's as if the Nephalum embody Anu's power and potential prior to him shedding his dark half. Like the Universe has almost come full circle with the impending rise of the Nephalum. Good and Evil have finally been reconciled into a single species again.