If Petaia and Campbell are both still at the Reds and it becomes clear that both of them are first-class fullbacks with equal opportunity to play 15 for the Wallabies, I'm sure the centralisation model would push move one of them to another franchise (with compensation provided to the Reds) so our best players are playing in their best positions each week.
I don't think it's about Rugby Australia necessarily dictating those terms though.
I would hope it would be tbh. Unless you have a Leinster situation, starter quality players in positions of strength should be shoved around. There's no point in the Rebels having Tupou, Pone, Talakai and the 15 months from eligible Eloff all capable of starting at Super level at Tighthead when the other super rugby sides have 7 "foreign" props on the books.
The SRU has, a month into the URC season, moved BIL Ali Price from Glasgow to Edinburgh because there's not the gametime to go around for all three of him, George Horne, and Jamie Dobie.
There's more to work through than that alone, but if RA want both Campbell and Petaia starting at Fullback rather than one of them spending time in the wing/centers, that should be their prerogative.
Of course, if we want to tear super rugby up and start again, different matter.