It seems like a RAAUS Recreational Certificate would only be necessary if you wanted to use one of their planes from their clubs? Whereas a RPL would allow you to fly an aircraft within the RPL privileges.
Raaus don't have "clubs" as such, they have flight training facilities of which some of those facilities have clubs associated with them.
Put simply, if you want to fly an aircraft with numbers on the side, you need a Recreational Aviation Australia issued Pilot Certificate.
If you want to fly an aircraft with letters on the side, you need an RPL or a PPL.
If you want to fly an aircraft with numbers on the side into CTA/Class C/Class D, you'll need an RPL or PPL in addition to your RA-Aus Pilot Certificate.