Exactly why I wouldn't do it. If house supplied power is insufficient, then bring in a power source that is.
Mix and Match with electricity is a bad idea.
I may consider lights on the house line and sound on the generator - but, first choice is to run it all off of a generator and not touch the house supplied power.
"Pardon me, neighbor, might I borrow a barrel of megawatts?"
I've been venue electrician for a televised, scripted form of athletic entertainment where the arena and live audience is part of the set and dressing, but the real product is the TeeVee stuff. Redundant generator sets that power all tour needs, with 1200 amps 208 3ph from venue to the transfer switch. Somewhere in between was the biggest damn "UPS" battery bank I've seen that wasn't bolted down. In winter this has to be in conditioned space, and I recall a bigger-than-usual fork truck brought it to move it.
But yeah, shore power was the 3rd choice... I guess grid electrons ain't good enough for some folks!
