yeah, however these types of jobs have existed for a long time. That is what Nate Silver of 538 did before doing what he does now. He might still do it too, don't know though. So, I assume, they have contracts and other methods of mitigating that conflict. I also assume that clients/employers do what they can to know if someone like him is trying to fuck them over. There are probably some pretty nasty consequences for getting caught too. I doubt they can ever get rid of all risk but, if the person is good, I imagine the risk benefit analysis falls into the favor of using people like him. You will find these types of entities scouting university math departments, especially statistics majors.
The odds for lots of sports betting literally change based on the bets made. Bookies, legitimate or not, shift the line and odds to account for the money on the line - they're never going to lose money if they can help it. The house always wins.
If there is a way to make money there will be a industry made for it. If there is an industry for something there will be consultants for the businesses in the industry.