Well yes its possible to bypass launcher if you understand what you are doing.
But if your server has already password, what launcher enters, then it keeps away most of the hackers or more like people who want to have fun.
You can also create req yourserver.com/createsession.php?username=characterName and it returns unique username so now launcher connects player with server and ingame is checked that player got his name from launcher.
But it wouldn't be bad also to add ingame anticheat for the baddest cheats like vehicle warping, guns and airbreak, if you cant shoot vehicles to other players then you have almoust built perfect anticheat.