I have played on PPP for quite some time now and if there is cheating going on, I would suspect it happens at PLO4 or PLO5, but even there, I staked a lot of players and they all did very well (beating games at 8evbb+).
At NLHE, it would be a lot tougher to have any influence on the game unless the cheater has like 3 accounts on a 6max table.
Club owners do not have any tools to verify if cheating is going on, but players can tell their agents and he and the owners can decide to do something about it or not. Hand history mining is available too so it could help to verify claims