A couple of points- I really do not think that the hydrogen plays a huge part in refrigerator fires- the ammonia is flammable as well, the hydrogen is at the top of the unit, not at the burner, and there just isn't all that much. While it certainly adds fuel to the fire, it isn't the main danger.
The other point is that many, if not most of the fires are from simple overheating. The refrigerant leaks out and the thing gets hot enough to ignite surrounding materials.
I'm kind of ambivalent about the Atwood refrigerator (and air conditioner). Probably not many here remember the Atwood refrigerators from the 1980's- I worry about orphaned appliances, like the Carrier air conditioners.