When I got my BiPap machine they gave me a bunch of paperwork with it that included the same warning. They consider your CPap to be a life support device and as such figure the same rules apply as used by hospitals. They're just covering their backsides.
As for how to power the machine, in my last two rigs I just used a DC outlet by the bed powered by it's own group 24 battery. I used the separate battery because my old Machine would sometimes shut down when I got a semi low voltage situation occur when the furnace kicked in.
For my current rig, I simply have a 600 watt pure sine inverter I run all night that powers the whole 5er. Doesn't draw much power really and works good with my setup.