Cultural referents for everywhere else are pretty obvious, but I'm having trouble with Noos. 

It's Bronze Age, very insular, they use galleys, wield sickles (khopesh or falx, maybe?) and wear armor with lamella and bronze dish (I can picture this and I swear I've seen it illustrated somewhere, but I can't find anything like it now).  The galleys and bronze weaponry make me think Mediterranean, the elongated skulls seemed Mesoamerican at first (but after doing some research many Greek writers described "Macrocephali" living near the Black Sea.) 

It's obviously tied into Atlantis, so it *could* be anything - are there references I'm missing? What are other people using?

More concretely, is Kovatos the "weird god of the Noosfolk" that the Deathless wants to see killed?

At my table, I pull heavily on bronze age greek aesthetics to describe them. But as you mentioned, due to a few factors they're very much anything goes.

The Deathless isn't working with perfect information - indeed, few are in Wolves. In this case, Kovatos definitely satisfies the mission.