Please excuse my raising of the dead here, for the sake of information.
I have a "Junyize" brand 5kw hydronic heater sitting in a box waiting to go into my E350 - it is as of this writing marketed by multiple off-brand companies like Hcalory and come-and-go in availability. So far I've bench-tested the unit on diesel and 85-octane gasoline, with decent results on both fuels. I've had similar experiences running the cheapo diesel air heaters on both diesel and gasoline. As my van is a gasser, I'll be fueling both the hydronic and (backup redundant) air heaters with gasoline. I've got a pile of older China heaters in the shop, a few of which were specifically marketed as gasoline heaters, and I've found no difference in hardware or controllers between gasoline and diesel units. Also, the Junyize manual (comically in Engrish, Russian, and Chinese) mentions the mid-size 5kw unit I have as able to run on diesel and gasoline, but the larger and smaller units are listed for diesel only.
Per high altitude fuel adjustment - I have had success with a small needle valve between the fuel pump and heater at roughly 9,000ft. The pump and heater both aren't equipped with the appropriate hardware or software to care, and do not complain.