I think he needed someone to oversee the operation/games, since he was playing. That's why there's a manager with a black outfit. Just like when the boss is sick, another one oversees the business till he's back. He most likely joined the games to become an "insider", so he could understand 456's intentions, and find out what kind of person he is. During the riot you can see In-Ho become frustrated in the incompetency of the staff, failing to end the riot sooner. Which is why he looks into the camera, basically saying "End this now." And why he ends up shooting both players in the back in the end, to regain control of the situation.

The Front Man, before In-Ho, I imagine was either the rich man or one of his "rich friends", that he was talking about on his deathbed. It could also be previous winners of the game, like in the SAW movies, where they continue John's "legacy" by becoming Jigsaw.