I think no-one who has been registered or who has obtained a teaching qualification is allowed to.
It depends on the competition. Registered dances are allowed to couple medallist dances and i think this generally goes for most competitions in Victoria. I thought i read on the Ballarat competition that teachers are able to couple medallist students but are not able to have been their coach, or something to that nature...
Ahh. Don't mind me. I was getting confused with Registered dancers actually competing.
I think I've read that only registered dancers of level 3 or below are allowed to partner.