FWIW, I would not want drywall in such proximity to a moist environment, at all. I think code most everywhere requires at a minimum, green board, though that's still not entirely water resistant. Mold is such a problem, I'd want to just do it right. I'd even go beyond green board, personally. Admittedly, I'm a little new to all this, but what I do know is pretty easily thrown out as the fact that the potential damages of mold and water permeation are far greater than the cost and hassle of changing out ill-placed drywall whenever possible.