Wisconsin has a compact which does specify minimum payouts for slots. Basically an 8/6 for Video Poker and something right near (slightly above) that for "reel" slots.
The foxes watch the hen house, or lets say IF something a bit unusual happened, for example decks being shorted on 10s, they would get a slap on the wrist. This was the tiny backwoods type casino. The big ones with major gains at risk, would not venture into anything that loses credibility.
It appears that Illinois and Minnesota have major corps. operating the casinos, but I'm not sure if it's some or all.
As far as I can tell, all Wisconsin casinos are "tribal owned", even though they might have partnerships with investment groups.

I don't even think they have public reporting of profits like many other states.