It looks like most tribes do operate gambling ventures.
According to these sites, out of 336 Native American tribes, 213 have gambling ventures.
Which is true: most tribes operate gambling ventures or most tribes do not?
2 answers
http://www.pbs.org/indiancountry/challenges/casinos.html
http://www.artnatam.com/tribes.html
http://www.artnatam.com/tribes.html