As Dingo says it is kind of indirect heating, only times I can think it would be useful is if you are already using a hydronic (either for main hot water supply or for auxiliary/pre-heater in the engine coolant system) so would save a bit of space/cost on installing an airtronic. Living in Scotland I have considered adding a hydronic for pre-heating my engine in the winter but it is way down the line after the repairs, and since I already have a D2 I probably wouldn't extend the circuit for heating. I might consider adding a calorifier for hot water but I need propane for the stove so might use a propane water heater, if I get fed up with heating water in the kettle.
I'm not sure a towel rail radiator would be ideal in a motorhome/RV - those things are not exactly built to be light and you will normally want to fit it in the wet space so with the door shut it won't do much for the rest of the van! The radiators used in motorhomes/RVs are usually compact things, often a load of 3" square thin aluminium fins along a length of pipe, although the eberspacher ones are more like a small heater matrix with a fan. The main concern with them is placing them where they won't get kicked or bumped because the fins will bend.
Now, if you were talking about laying loops of microbore pipe under your flooring and using the hydronic for under floor heating, that might make some sense - electric under floor heating will take up less space but I doubt it can be run from a 12V battery.
Central heating is great in a building with lots of rooms because you just need one heating plant to supply them all, but in a small sprinter conversion you often only need one heating outlet, maybe in a larger motorhome with separate bedrooms or a boat with different cabins it is more useful?