Consider installing a zigzag xfrmr to establish a referrence neutral and dropping in a GFCI MAIN breaker.
Delta pretty much requires a knowledgeable player on site to jump on faults. Since this occupant is not a manufacturer there is scant chance of that.
However if the customer is using 480 solely for lighting and A/C they probably won't bite.
The danger is if their maintenance man plays with the high bays and screws up. The significance of the indicator lights has to be driven home. I'd wire in an alarm contact on each branch of the indicators: stop working on the system -- call electrician immediately.
