The admins must be known and there must be a topic to list all of them, a newbie hacker won't be visiting the forum to check it, a newbie hacker won't hesitate to cheat if admins are online or not, he will cheat and get banned anyway..
Do you remember when I banned you while I was undercover? Even it was a little rule break, regulars attempting to take advantage while no admin around in server.
So think about when an hacker able to check if any admin online in server. If hacker finds out there is admin online, he will avoid to use hack. Then it will take ages to check him by admins. That's why we have privacy about admins in server.
About forum, if he is ban evader already, he can simply go to forums and check the admin list. Then he will take a note for to not join game while those admins are ingame.
Does that makes sense now? Never say never