Yes SuperGrover is correct Connacht, for the moment and at least a few more years, have different rules to the other 3 provinces.
In Connacht there's a move to change it from being a development province which in principle meant giving young talent a go earlier than they would at the other 3 provinces. But in reality meant it was the graveyard players went to when they couldn't make it at the other 3 provinces.
Now they're focusing on becoming more competitive and not proping up the Pro12 every year like they used to. They aquited themselves well in their first HEC campaign this year and have shown signs of improvement year on year over the last 3-4 years.
Allowing them to have more foreign players I think is a good thing as it means they can continue to be more competitive and it means that Irish players who make the starting team are, generally, of a higher grade and more likely to be in consideration for the national squad. They still have a lot of work to do before there will be Connacht players regularly in the national squad but they are moving in the right direction.
I would see a similar path of development for the Rebels working well. Denying them the services of a few extra foreign players would be detrimental to that development. Most of the best talent has already been cherry picked by the more established Aus franchises. Forcing them to pick players who are not up to S15 level, just because they are Australian, is not going to make them more competitive.
However neither do you want them to become a mercenary franchise that is dominated by foreign players. I think for their current stage of development the balance is about right and would expect that once they become competitive on a more regular basis that they'll fall under the same rules as the established franchises.