There is a Check Valve on the Hot Water outlet side of the Hot Water Tank. This is to prevent any cold water from the RV's plumbing from backing into the Hot Water Tank.
I am 99% sure that the check valve on the water heater is really there to prevent antifreeze (or any other fluid) from flowing back into the water heater when the water heat is bypassed.
Our check valve was replaced with a ball valve and we have had no issues with water temp.
I am not familiar with home water heater ever having a check valve on the output. Homes, do have a anti-siphon valve to prevent main line contamination.
The water system has to be a hydrostatic system, thus the pressure of the cold water entering the tank is the same as the pressure of the hot water leaving the tank.