Anything is possible.
If you can or want to give up the extra wall thickness then go for it.
Some concerns that I would have?
Burying heater hoses in an inaccessible space. Why? Because eventually those hose are going to wear out. Whether rub in specific areas or just wear and tear because every time the coolant heats up they expand and actually stretch out some and as they cool off they contract and draw back? Options to help are while they are exposed you can re-route the hoses under the bus, change everything to hard pipe in the wall with tubing at the ends with access or new rubber tubing at a minimum so then as you take the old stuff out you can look at its condition and guess at how long the new stuff is going to last?
NOT TRYING TO SCARE YOU but I myself would not want it buried in my finished walls and not know I have a leak until my finished floor is showing signs of something leaking and my bus engine needs a gallon of fluid every couple of months?
The only other thing is to be careful of how high you raise the heater coil in concerns with the top of the radiator of your engine? Why? Because towards the top of your radiator there is/should be an overflow jug/tank that handles all the air and fluid during the expansion and contraction of the fluid in the coolant system so in my mind if you get the heaters elevated above then you will have a problem with that fluid wanting to drain back out of the coil to the radiator which will send it to the overflow tank. Which will leave air in the heater coil which won't show up at first but it will show up as the coil not working. The cause will be that it is air locked and can't move the coolant. Even with a secondary pump if the air has gotten back/into the pump.
There are several options to expand your idea if you will give us more info.
I don't have coolant heaters in my bus?
I have been doing commercial steam,gas,and hot water piping since 95 so the ones that do have coolant heaters in there build should chime in in a little.
My thoughts and opinions are from my work except burying rubber radiator hose in a wall with no access in a finished SKOOLIE. I would never be able to sleep? I would be like a dog constantly looking for a problem to protect what I had?
Don't know if the dog thing was a good analogy but mine will let me know when a piece of trash is blowing buy?
Good luck