Nasty problem there is that a nuke might kill off the normal zombies, but any survivors in the area, and any normals who enter the area afterwards, will be horribly mutated by the radiation and become radioactive zombies. That is sort of like trying to overcome a flood by purposely opening a dam.
As for a Metal Gear, if we are going to add fictional weaponry then there would be better weapons still. Like, I dunno, a cure.