I, too set knife to mouse wheel (except down, as opposed to up for you MaydaX :P). The only problem I see is with mouse wheel +attack bindings and single shot weapons.
In fact my clan is due to have an admin meeting soon - and I intend to discuss whether we start kicking/local banning for it. The way I see it, it is an exploit.
It is indeed a hotly debated issue, and I think it will remain at the Admin's discretion as to whether local bans are handed out. I cannot really see any anti-cheat software kicking for binds - unless a custom CVAR check script was introduced. Even then I cannot see it being adopted by all admins - and I cannot see that everyone will agree on whether it is bad or not!