Sure, it happens all over the world. Jetstar is a bad example, it's a Qantas company. A better domestic example would be buying a Qantas ticket and ending up on a Cobham aeroplane. But so what? It's not like Qantas try to hide this from you.
Remember the 717 at Darwin recently? Much was made at the time here that it wasn't a Qantas aircraft despite the paint job. And it would have taken a knowledgeable punter a bit of digging on the QF web site to find who owned and operated the aircraft. Not immediately obvious.