Community manager roles do more than just sit in discord. Aside from being the communication line between community & developers; Their roles typically involve dealing with and managing social platforms(forums, steam forums etc), writing up blogs and other news related posts, dealing with ban/exploit reports and pushing to the right places etc
Community managers typically also have a direct line to EAC tools to check for alternate accounts or account status with EAC(Account flagging etc).
This is pretty much industry standard for CM's. A lot of CM's play the games they're involved with too, also not uncommon. If a CM is serious about his/her role, they'll remain as professional as possible and not form a bias when doing their duties.
GM's playing the game they're policing is a different story, due to the more general insight and actual in-game power they have with the game.