I don't know that having a certification as a credential will necessarily help you get admitted to a masters program - I do know that some schools will accept it either as credit once you're in (in lieu of taking a class) or at the very least use it to waive you from requirements... but you might check with the program in question that you're considering first.
Either way, I don't think I'd seek out certification purely on the basis of 'it might help me get into school'.