Well, theoretically you can be an atheist on Golarion. Someone who says "Gods? Sure I know them! Here is this Razmir guy from Razmiran, who is, in fact, just a powerfull wizard. What's difference between him and your gods? They can grant you access for divine magic? So do demonlords, empyreal lords, the four horsemen... Hell, it seems like even a chicken can grant you access divine magic as long as it is from some outer plane! Face the truth! Your "gods" are not divine beings just some magician who can do better tricks than other ones."
There is difference between knowing that there are some powerful beings out there who call themselves "gods" or acknowledging them as, well, gods.