The purple cloud doesn't mean you have their agro. It just means that the monster/character got slowed down (Although that does mean you connected with provoke).
I've yet to see a monster/boss that isn't affected by provoke. Every single thing I've tried it on works.
EDIT: Also, moved to Sieg hunting grounds.
Last edited by Gladiat; 09-24-2009 at 10:54 AM.