I guess if you want to accurately want to do the checks on the server side you’d have to run the complete game on the server. You can cheat just by making a texture transparent so that you can see enemies behind it. To prevent that the server has to render the frames itself and to ensure that really only approved things are seen by the players the easiest would be to just send over the rendered frame instead of letting the players render it themselves. By that point you have basically invented game streaming again.
Still, I wonder what Blizzard games are doing. They work fine on Linux and I haven’t heard much about cheating on there.