As an ex operator at Movie World, it was actually fairly common for staff to be rostered earlier for media filming etc. So this is certainly something that they do offer. They did it for Theme Park Review, as well as a multitude of local media channels as well.
Generally speaking, except for a few positions cast sign on time as a ride operator (not a supervisor) would be 9:45am clock on time. This allows 15 mins for the operations opening checks to be done (estop, sending with harness up, gates open etc). as well as completing 2x full cycles of the ride. This is easily able to be done in the 15 mins before rides open at 10am. Certain positions would require a earlier start, such as Superman rostering 1x cast member to start at 9:25am to act as the entry host and Scooby having a 9:15am start to dot track walk with the supervisor.
So yes, paying guests would not have been impacted general operation of the park at all. They would have likely gone through the gate, straight to DC rivals and done their filming before 9:30am. The staff instead of starting at say 9:15 AM (due to extended hours) they would have started at 9:00am so they can do the opening checks until 9:15, then 15 mins for filming and then open at 9:30am. Worst case scenario, the ride -MAY- have been delayed by 5 mins or so but nothing major at all.