Yes they are. Every university except USyd (long story here, they kinda got kicked out) is part of a consortium and they all run through ACER/GMAC and now GEMSAS.
Heh. Up until this year, it was 3 universities max and 1 interview max (in reality if you didn't interview at your first preference you wouldn't get an interview at #2 and #3).
This year, GEMSAS was created to address this problem. You can now list 6 preferences, but you will still only receive 1 interview. Interview scores will be standardized and passed on to lower preferences if you don't receive an offer from the school you interviewed at. That's the good news. The bad news is that because of this, it's now much harder to get an interview/place, because you're competing against everyone, not just the people who put your school at #1.