The Devs have ample tools that if they don't want you to be able to move a mob you won't be able to move it or it will simply reset position when the event starts. In 2004, let alone 2014, this is a complete non-issue. During Velious in order to let a raid position itself a mob would sometimes be perma-rooted and until you took it to 97% would do nothing to players outside of melee range. The most infamous abuse with BFG was moving Yelinak.
