Welcome to the forum from extreme Eastern Va. Yeah the only way to check the hot water heater would be to fill it, turn it on and see if it heats up, then drain it after. As with any used RV, look for any signs of leaks inside the unit and check the roof/sealant condition. Also check the floor for soft spots. Since that is a hybrid, give the bunk doors/seals and tentage a good look over as well.
2004 Chevy 2500HD Crew Cab 6.0l, 4.10r
2010 Jayco Jayflight 28BHS
Reese Strait Line with Dual Cam
P3 Brk controller