100%.My take on it is that Maori in NZ are over represented in the lower socio economic group in the country, though not limited to just Maori there either. This is likely because of a mix of historical issues, lack of role models, education, victim mentality, members of that group keeping them down, lack of ambition or drive to better ones self etc. That group would seem to me to be more likely to be committing crimes for a number of various reasons and therefore over representative in crime statistics. Add the problem we have with 501s being deported back here, though I would consider this a fairly low percentage of the problem.
Those who move to Australia seem more wanting to better themselves or their circumstances, remove themselves from their current environment, possibly have more ambition and have achieved a decent level of education. They likely move with a job already lined up. Probably more likely to be driven, focused, less of a victim mentality and a desire to succeed with a limited safety net available to them.
Take Pita Hiku for example. He himself has said that he needed to get away from his environment to succeed. He had mates here wanting him to get on the piss all the time. Without moving out of that, he would have been just another could have been good player.
The percentage of Maori in NZ prisons is not dissimilar to the percentage of Aboriginal and Torres Strait Islanders in Australian prison. I would expect there are similar concerns and issues driving this as well.
In my opinion, a focus on education and lifting productivity is the way forward. Specific policies should be made on low socio economic group rather than on specific ethnicity or race. While historical issues and injustices are obviously a cause, when do they become an excuse rather than a reason for outcomes? An environment for a self fulfilling prophecy? I feel we are near that point now, if not there already. 170,000 Maori doing well in Australia would seem to be a very good indicator of that.
My guess is that Aboriginal and Torres Strait Islanders in New Zealand would have the same marked reduction in prison rates as Maori in Australia.