Question - To legitimately log co-pilot hours on something like a PA31, does the operator not have to have CASA approved multi-crew procedures?
Nope. We had single pilot ops but if the autopilot was u/s then you could carry a copilot and then fly IFR. That was in the DDG a CASA approved document. The copilot had to have a minimum of a current IR and a endo on the aircraft.
Some mining companies also stipulate two crew at all times. How are you going to log that?