Look, its never a bad idea to sign a celeb from another sport, tv, movies or whatever for a plublicity rub. Sometimes it works sometimes it doesn't. WWE did if for years. Its not a big deal. I mean we had Mike Tyson, we've had Ben Stiller put in the figure four by Jeff Jarrett on Smackdown once, we even had much to everyones suprise the very sucsessful Kevin Federline. Some work well (like the K-Fed & Tyson), some people don't really remember, (like the Ben Stiller). The catch is, you have to make sure your using them properly. Getting Bobby Knight is not a bad idea. But to bring him in permanently might be a little silly. Bringing him in for one or two appearences to maybe help put someone over or to be a celeb manager for someone, again that might be okay. But to bring him in permanently as the Coach of TNA, seems dumb.
As someone said, it could get some plublicity from ESPN and so forth. Just as when they had the thing with the Chicago White Sox. It gave them a little press, but ultimately they are small gains. This is why it should usually be a one shot deal with non wrestlers. Because anything else is probably too much for little gain.