did you try debug?
Code:
on *:NICK:{
  echo -a nick change, $nick > $newnick
  echo -a userlevel, $ulevel($address($newnick,5))
  if ($ulevel($address($newnick,5)) == 6) { kick $chan $newnick Attempting to use a profanity nick is forbidden in this channel } 
 else { halt }
}

and then look at the echo and see if it's a match, the $ulevel would be the part i guessing dont work for you.