Well they do auditions for actors for Horror Nights. Last year there was the person in Containment on the truck, he was an actor, and also the man outside of Cirque Du Freak who spoke, was also an actor.
Same goes for two years ago with the Wicked Witch and the Caterpillar.
As a matter of fact auditions for a similar type role (Actor A's for HHN) is being held soon.
http://www.universalauditions.com/ORLANDO/schedule.asp
I wouldn't rule out that a potential actor for an icon could be selected from this audition.
Pure speculation on my part though.
What I said before still stands though. If old icons were to be brought back, Universal would try to rehire the actor who originally played the icon first.