My main concern with Glenn in the game instead of Henry has nothing to do with pass defense - it has to do with forcing the corner on the run. Glenn is a quality corner who still probably has the best cover skills of any DB on the roster - better hips, feet and ball awarness. His gambler mentality gets him in trouble sometimes, but overall, I have no problem with Glenn defending the pass.
Glen's play vs. the run, however, is nowhere near as strong as Henry's - for obvious reasons. Glenn can still heard the run inside, but Henry can actually attack the the corner and force earlier decisions by the RB.