Sorry, but it is not illegal to be paid as a jump pilot in Australia.
Parachuting is expressly defined as a private operation, thanks to some very effective lobbying by the Australian Parachute Federation some years ago. But this does not place any restrictions on the financial relationship a pilot may have with a drop zone operator.
To illustrate, if BHP were to operate a bizjet for the transportation of their staff, and the accommodation on the aircraft was not available to persons generally (CAR 206 RPT) and no non-BHP legal entity was paying money for the accommodation on the aircraft (CAR 206 charter) then that would be classed as a private operation. The pilots would of course be paid for their services. This arrangement is entirely legal and bona-fide.
Now although your jumpers are paying big bucks to the drop zone, because of the special status of parachuting, it is still classed as a private operation. But that does not make it illegal for you to be paid.
It is of course your right to decide that you are happy to fly the jump plane for no pay. And it is of course the drop zone operators right to decide that the no pay arrangement suits him too.
But please be absolutely clear that it is in no way against the law to be paid as a jump pilot in any Australian jurisdiction.