Installation

No, the instructions recommend you don't.

This is a re-circulation pump. It is designed to be installed directly on the outlet pipe of your tank water heater. It will not boost pressure, work with a tankless water heater, or any other situation.

I guess so, but I don't know for sure unless you are talking about the supply line coming into the water heater. If that is the case the answer is yes. My supply is a vertical line.