The native tribes want to take over the horse racing industry?
Pari-mutual wagers are generally associated with horse racing (and dog tracks I suppose) but there maybe others as well when there are multiple entrants in a contest. The money bet on a race is put into a pool, from which the odds are calculated based on how much is placed on each contestant, with the house taking something like 17% off the top and then paying out to winning tickets according to those odds.
The way I read this is that the tribes have exclusivity to sports betting (football, hockey, etc...) but parimutuel facilities want in. Horse racing is separate.