Of course, that has always been the argument. Why do you think First Nations are allowed to own and operate casinos? The argument has been that gambling has always been part of their culture before everyone from Europe showed up.
http://www.lazchar.com/2016/04/11/aboriginal_first_nations_gamibling-law_canada/
Now if you want to argue that this history has nothing to do with owning and operating casinos, I don't think I'd argue that. Don't at all agree with the lawsuit. But the precedent has been set in Canada and the US that gaming is part of the First Nations culture.