The simple answer is "NO".

T&P valves are BTU rated to match the BTU rating of the burner or heating elements and the drain line must be equal to or larger than the output port of the T&P valve.

If that closet has a wooden floor or a floor material that can be damaged by water you must also have a drip pan, and the pan must have a separate 3/4" drain line.

Also, you may install an electric water heater, but if you have a solid, liquid or gas fired water heater it may not be installed in a closet with the AC unit unless all the return air for the AC is fully ducted through the closet space from the adjacent rooms.