The default player.JSON value should be set to: "Monitor AI Postfix":" (AI)", "Monitor AI Postfix#":"what is displayed after AI driver names in monitor (multiplayer only)", You should see (AI) after each driver name in the list, while on the server.
One thing to consider though is that once a person leaves the server, but stores their car in the garage the server will identify them as AI until the end of the race weekend/session. (I am assuming this is a known bug)