I go to one in Howick which is about as middleclass european/asian as you can you get

I went along because the girl that runs it is one of the old school maori families around here and they lived up the street from us since forever!
Ours is probably different to most however as our base is being torn down and we're meant to be moving to the whare when it is built so atm we aren't really talking or doing much learning in maori. But I find it great for support, and friendship and the kids love eachother, we're a group of 5parents and kids one guy comes so he does well to come when he's surrounded by girls

but he's friends with two of us from school.
I find it refreshing as I have come across prejudice alot since I was a kid growing up here and I know that one of these families has found most of what I've come up against we went to the same schools and that sort of thing.
Even though we aren't doing much in maori atm I am still using bits of maori and DD understands it as she does Samoan because I use that too.
I wouldn't worry about not fitting well, unless its one of this click clicky groups which tbh any playgroup/playcentre/mainly music has potential to be then you should be made to feel welcome. Oh and DD is half cast Samoan part maori and european. Ours has had indians, south african's, europeans and our half cast islanders come and go.
All you can do is go and try it, give it a couple of sessions if you don't like it you don't have to go again. They won't talk solely in Maori I wouldn't imagine as that is more a kohanga thing. They will probably do simple activities and counting games and songs like we did as primary kids.