The UOA/Voldemort messages a player sees don't have anything to do with the server, so the server can't detect them. The client can, but presumably if the client was made to check for odd messages, then the Voldemort program would be made to prevent the check.The tell is actually whether a person can hit the hokeys at 0.1 sec intervals consistently 100% of the time while running around toggling specials/casting spells (I mean at the same instant), and oh I don't know, trying to repeatedly drink potions when they have run out (while casting remove curse at the same time) or have customized messages (different from the UOA message) telling them they have run out of a certain potion. That would be a dead give-away.
(Though it does strike me that a lot of bans could be handed out before this was discovered. I dunno though, can UOA display custom messages for other events? If so, the idea is moot).
Re the "0.1 sec intervals consistently 100% of the time", unfortunately no one can do this - regardless of their methods - due to lag.