Can someone still be an athiest if they believe our universe is a simulation?

[afleitch]

Yes. If we live in a simulation our subjective reality feels real, but it is in fact objectively a simulation. Someone may have created that simulation but that someone must live in either 'actual reality' or perhaps is also in a simulation. It cannot be godlike if it's also a simulation. Nor can it be considered so if it's subject to a reality outside of it's self which it doesn't have domain over.