Just because someone is a good player at their position doesn't mean they'll be good on special teams coverage and vice versa. Eddie Drummond returned a kickoff for a touchdown, but don't let the #18 fool ya, he's one of the leagues best return men. He's also had several opportunities to change his number, but has stuck with that one for whatever reason.
If you want good special teams coverage guys, go get Jimmy Wyrick, Jeff Gooch or Rod Babers...they'll come cheap. These are all guys who have excelled at it. But don't stick a starter in there and risk injury, when he probably won't be as good at it anyways.
And just speaking on the concept of using starters, I think Dunta Robinson would be a better coverage guy than Aaron Glenn anyways. Of course you'd never know until you saw them in action, but Dunta is faster and is a good sound tackler. He's also got a little more size it appears, thus making him a little harder to block and move out of position. I'm assumming AJ stands for Andre Johnson, and unless it was the last play of the Super Bowl I'd go with 10 guys on my coverage team before putting him in to cover a kick...but maybe that's just me.