Roy,
You will NOT be allowed to run any non-CAMS/FIA approved or expired harness in any CAMS speed event if the scrutineer follow the CAMS rules. You would most probably be asked to removed them and use you OEM seat belt if equiped, most OEM 3 points seat belt is ok for CAMS non-race speed event.
You cannot compare the effectiveness of the standard OEM seatbelt to a 4/5/6 points harness, when you are in a rollover.
This car was 3 meters in the air rollover a few times the car had no rollcage but the driver had 4 points harness. He survived and was very glad to have had the harness.