My father in law used to be a logger and used the "warming fire" trick all winter to get his skidder running. This was before the days of being able to hook it up to a running truck.
As far as cold starts, here in northern NH we have already had a couple -20 mornings, and my trusty Cummins started right up using the grid heater. I think it would have started without it, but I like giving it extra help. I'm shocked by how well it starts in the cold. MUCH better than my '96 Ram.
As for the ether, I wouldn't take the chance with an expensive engine.
Jim