the battery boast switch in many RV's is essentially this. They bridge in parallel the house batteries to the chassis batteries to aid in starting the motor when the chassis batteries are drained.
it's not something you should do often or for long periods of time as deep cycle batteries weren't designed to give that many amps that quickly, but yes you can. the factory is already giving you that option in class a and c rv's for sure.
himcules (10x stronger than hercules)
2013 Forest River Berkshire 390BH-60
ex 2007 Jayco Greyhawk 31SS