You may want to check out this link before joining this group or any others. Whilst I'm not a member of this site, it can sometimes be an eye opening read.
http://www.newagefraud.org/smf/index...13560#msg13560
I also depends on what you want, if you don't mind paying a group like this and getting a certificate at the end of a few days course then give it a go.
Or you can talk to real Natives and learn what they are willing to share for free if they are inclined to do so.
Its also worth remembering Native beliefs are not Shamanic beliefs they are different and from different part of the world. If you get it wrong you can end up upsetting a few NDN .
Many NDN's are naturally now very protective over there beliefs and ways, because of this reason and you have to get to be respectful and get to know some first. If they choose to then share some things about their beliefs with you well and good.