During the song 'Red Solo Cup' the drummer is sat on the floor building a tower out of extra cups but the height of the tower changes between shots until it is knocked over by Artie and Puck.
(at around 8 mins) The camera guy can be seen onstage to the left, with his back to the New Direction dancers downstage. He's filming upstage towards the band.
During the performance of man in the mirror, you can clearly see a cameraman and crew member