Will and air hammer work as a concrete vibrator?

An air hammer with a blunt bit and reduced air pressure will work fine.

If you have access to a welder you can use a worn out bit and weld a piece of plate steel about 2-21/2 in square (or round) makes a very good tamper also

This method works best.

Put your concrete into the mold. Push the concrete down into the mold and keep shoveling more in until the mold is completely full. By pushing the concrete into the mold there will be fewer air bubbles trapped in the mix. Press the concrete down into the mold with a float then smooth the surface with the float. Using a straight piece of wood (the narrow edge of a 2 by 4 works well) screed off any excess concrete by moving the wood back and forth in a sawing motion as it is slid across the top edges of the mold from one side of the mold to the other (angle the leading edge of the wood up very slightly). It may be necessary to remove large pieces of gravel that poke out and shovel in a small amount of concrete to fill in voids that appear.

Once the mold is full and level, begin hammering on the mold with a plastic or wooden mallet. Air bubbles will appear at the surface. Keep hammering on all sides and the bottom of the mold until bubbles are no longer appearing. Then take a small orbiting sander (pads covered by a rag) and run it all around (under and all sides) until you do not see any SMALL bubbles coming up. Trapped air in the counter will result in a weaker counter top.

After the concrete has set for a couple of hours, trowel the surface with a metal concrete trowel. Do not trowel to the point that puddles form. Wait to completely set and remove from form.

Concrete vibrations...ok, it may not be a question, but below is a video of the answer

Yiou would need to replace the tip with a very broad plate and reduce the air pressure.

To hard it will cause seperation , which will weaken the mixture. buy a pencil vibrator