I doubt he used the bump stock on the shots he took toward the petro tanks.
Since Paddock didn't use the tracer rounds, we don't know what he intended to do with them. Paddock obviously intended to use the incendiaries when targeting the fuel tank. Since precision would be required for the fuel tank, I can see why you think that was the intended purpose of the tracer rounds.
Since the bump stock used on the festival grounds would have resulted in less accurate fire, my assumption was the tracer rounds were intended to help him target the festival grounds. Using a bump stock at a range of 1,000 feet would result in wide dispersion. Paddock probably would have been better able to achieve his evil objective and caused more casualties if he hadn't used the bump stock.