The Rescue Coordination centers, not the rescue pilots, will often stop, or try to stop other civilian/commercial aircraft from getting involved in a search. I have been involved in a few, and in NZ, and Oz would be pretty similar, when you are just doing a visual search, then you can be in a 22 for all it matters. A 44/206/500 etc, would probably be better, so that you can have an observer each side, and the pilot concentrates on flying, but anything is better than nothing.
I have been threatened by the Rescue Coordination Center in New Zealand with all sorts of crap, and basically tell them to f off, when the family of the missing people are willing to pay for extra aircraft to be put in the air!
Bureaucracy at its finest!
One time i was told that we weren't allowed to go in to look for a missing plane, as the rescue helicopter was in there, and the area was too small to have more than one aircraft. I said i would talk to them and we could maintain separation, no way, not allowed, and anyway as soon as the weather clears they are sending another rescue BK and an Airforce NH90 to search. But i asked, isn't the area is too small for another helicopter to fit in!! We went anyway and talked to the rescue pilots and they were happy enough to talk to me, but they did have a laugh after they had gone to refuel and came back with a message that RCC were trying to get me arrested by the local police, without any luck!