To run the air you need to close the windows etc, so if it or the gen conks out or fails to start the rig will be sweltering soon with everything closed. I would be nervous leaving. DW would simply refuse to take the chance.
If you leave them under a running Fantastic Fan with plenty of water they should be ok, and with that method you can have open vents and windows too.
It might also depend on the breed of dog what they can take. Better to ask on the RV Pet Forum what people do. They have lots of good ideas over there on such matters.
