I think all Atheists would be considered a form of Agnostic, maybe equalling a strong agnostic by some definitions or another subsect of Agnosticism.  Agnotic defintions vary so widely, that one Agnostic could believe in a God, while another doesn't. 

 The reason it could be considered a subsect of Agosticism is that an Atheist believes that God(s) do not exist, not knows they don't exist,  Anyone claiming to know for sure either way is ignorant.

The best we can say as logical thinking Atheists, is that based on our knowledge of the universe, we don't believe in the possiblily of a god(s).