I know that Rush, on their last tour, used an AT AE5400 (AT LDC) as the vocals for Geddy Lee...but they're all on ears, only a 3 person band, and their instruments go direct (except for most of the drums) so they don't have as much of a problem with feedback. Even so, the FOH engineer remarked that he's had issues with feedback.
http://fohonline.com/index.php?option=com_content&task=view&id=295&Itemid=1
(2nd article on the page, "Rushing Into Something New")