I guess to better ask my original question, why would a coach who has a contract who isn't looking for a job need an agent? After the ink has dried on a contract like lets say Grobe who has a 10 year extension, do they really need an agent if they aren't looking to skip to the next job? I guess I would just find it extremely odd if Grobe, Kelly, Gill, or Pelini had agents. There again, I don't know all the in's and out's of coaching contracts.
Almost all D-1 head coaches - and those assistants looking to be head coaches - have agents or represenatives. The reason is that no matter how well the coach is doing, sooner or later he wants or needs his name "out there". While you can be hired based on networking, more and more schools are moving to search firms. Those firms continually stay in contact with agents to know who might be a viable candidate when jobs come open.
A friend of mine has a son coaching at a D-1AA school. Obviously, he can't afford a full-time agent. For a time, I acted as his representative in some negotiations. That, also, is not uncommon for assistants in lower division schools - they know a lawyer or someone with a background in the field that they turn to. In their case, its more for legal advice than representation. But the head coaches often do have some kind of representative - it's the best chance they have to become known to D-1 ADs looking to make a change.
Also - and just as an aside - a lot of ADs keep notes and a "short list" of potential coaches. When an opening is anticipated, they contact the search firm. The search firm takes that short list and makes initial contact with the reps for the coaches on the list to see if there is any interest. In addition, the firm makes suggestions to the AD of coaches that it already knows are looking to move.
My involvement has been VERY limited - and I don't want to do it again. But man - the back room dealings are something else.