My two cents worth ...
Dash 8 gave a PAN on area (Centre);
Centre called the Airport Operator to let them know that the Dash 8 was returning with a failure;
Airport Operator was on the phone arranging Emergency services when the Dash landed safely;
Emergency services were recalled when the Dash taxiied in and shutdown.
I dont think there was a lack of comms here at all. Considering both the Ambulance and Fire are on the opposite side of Dubbo to the Airport it would still be 15 mins from call to arrival and by the time the Airport Operator was notified of the issue the aircraft was in the circuit.
Its my belief, and please correct me if Im wrong, but unless a pilot requests Emergency Services (with the PAN call) through Centre then it is up to the Airport Operators Emergency Plan as to whether or not they call Emergency Services, which in this case they did.