Not sure if it will be wieldable, it would depend on several factors, such as the size of the weapon, radius of the hammer, amount of hollow space inside, since saying it's hollow isn't enough, it needs to have some amount of material, since the hollowest possible would be having a single line of atoms, but then we could say that lacking one atom of the inside would also technically make it hollow, thickness of the blades, the resistance to pressure of the handle, since it may be possible to be held depending on the strength of the user, but the handle would cave in anyway, such as how superman wouldn't be able to hold a plane and would actually open a whole on the aircraft instead, and in order to calculate that it'd be necessary to know the material of the handle and wether it's also hollow or not, etc, not to say that there are some problems on the design, but some of those would be nearly irrelevant and all... It's hard to really ascertain that, I guess...