I've finally gotten to the bottom of the "Who is the guy on the bench in street clothes?" question, so I will share the answer so that we can all move on with our lives.
His name is Demetrius Williamson. He used to be on the track team and is a walk-on that is red-shirting this year. Apparently, he helps out the team in practice. Nick Berardini (this year's 12th man on the bench) did the same thing last year.