By Todd Cunningham LOS ANGELES (TheWrap.com) - Usher and Darius Rucker have been added to the lineup of performers set to hit the stage for Wednesday's "Healing in the Heartland: Relief Benefit Concert," NBC announced Monday. The show has been organized and will be headlined by Blake Shelton. Others set to perform include Luke Bryan, Rascal Flatts and Ryan Tedder of OneRepublic, as well as Grammy Award-winning artists Miranda Lambert, Reba and Vince Gill. Usher is a coach alongside Shelton on NBC's "The Voice" and is a multi-platinum recording artist. ...