It's rare for pilots to come from the airlines. RFDS is single pilot ops. You do work with a flight nurse and a doctor. (My sis-in-law's a Dr with them)
Mostly it's from pilots who've got some bush flying for a few years and then gone on to twin charter work, usually in the regional areas. A few have gone there after Coastwatch. It's usual to have a bit of turbine time before getting hired. Although, big piston twins are accepted too.
A few have left RFDS to go onto other things. One went to Antarctic Survey.
From the Desert to the Ice.