Could I put a vacuum breaker on the hot water side of a hot water tank if not why?

Why would you want to? The purpose of a vacuum breaker is to prevent the possibility of contaminated water being draw back into the system.

You mean a vacuum RELIEF VALVE, not a vacuum breaker. Here, a vacuum breaker gets installed on outside water faucets and lawn sprinkler systems to prevent backflow of contaminated water into the drinking water system... a vacuum relief valve is installed on the COLD water inlet to a water heater... basically opens when a backflow condition occurs and allows AIR into the pipes instead of allowing the water heater to be siphoned dry.

In my state, vacuum relief valves are required to be installed on all water heater installations. Most states do not require them, but they certainly can't hurt anything if installed.

The reason you don't install a vacuum relief valve on the hot side of the water heater is because it would not open and allow air into the system until AFTER the water heater got siphoned off... right?

Back to you...

Mark