Yes, the generator will start when the chassis engine is running when the coach batteries have been removed. I have done this after running the coach batteries down. The battery control center will engage the interconnecting relay and put 12 volts to the coach's system.
Be careful. Tape up or otherwise insulate the coach battery cable terminals because they will be hot as soon as the interconnecting relay engages, and may remain hot after you shut off the chassis engine.
2011 Sunseeker 3100
1997 Pathfinder Toad