Hah, I was right!

[VinnieJones]

You can still change what group raid members are in while in combat, but apparently you have to do it by hand in the raid panel. This is still a great tactic for filling groups with dead members that have specific roles ( ie. warlock imp) or giving certain groups (melee dps/ranged dps all of the bloodlusts on certain fights where they would benefit more from it)

Morg

[Garek]

Indeed you can! In addition, folks who are promoted as assistants can also change groups by hand.

[VinnieJones]

Hah! Promote the dead person and make them do it!:P