The head won't bounce back, because it's rigid.
You still don't get the benefit of any sort of follow-through because you're relying entirely on the stored momentum at the end of the lever, not any additional momentum from, say, your own body. That momentum/kinetic energy is all you get. This is why very light hammers are a bad idea, but a very light dagger works well.
You won't get the benefit of a swinging weight at the end, but you can still impart any force that you could with your hands. Depending on the surface area it would be like either a paddle or a rod, made of hollow steal. Armor would make it feel more like a paddle.
This is not true for the reasons stated above. A punch (or stab) carries with it the momentum of your own body, as well as continuously applied force from yourself continuing to push your body forward; you're putting your weight and momentum into it. A "swing" of a sword, mace, hammer, etc. only imparts the momentum imparted to the head of the weapon by the swing.
Daggers are different, yes. The main objective there is to cut.
It's true that hammering technique is designed to capitalize on the weight at the end, whereas a good punch would have your body behind the thrust. So you'd want to fight differently than with a traditional hammer. However, it's far better than a rubber mallet.
A carbon fiber tennis racket may be a better analogy than hollow steal, since those are lighter without breaking easily, and are designed to be light and strong.
