I've flown plenty of 91 legs for 135 operators, mostly repositioning flights that are not deadheads billable to the client (if a client pays for a round-trip charter consisting of a live leg, and a deadhead leg, I don't consider that deadhead to be 91, because the client paid for the leg, although it's empty). If the leg is truly 91, I don't see why the pilots should have to be 135 current. A trip for the owner is non-revenue flying, and the certificate holder (135) essentially becomes a management company if they retain operational control.