I literally linked to their website. Parker, CSA, and Eastman are the three I know of that are solid. Most ADs with experience just do it themselves and use independent guys they contract to conduct the searches.
To keep a hire like that a complete secret in the current media market is a massive accomplishment. Not only that, but they have the blueprint to do so.
To your second point, it's also not like OU was a poverty program. Dude had it relatively made there and could have flirted with other jobs to get his way, which is what these guys typically do.
ADs/Media guys all agree that it was a huge deal, especially in the way it went down. Hindsight is 20/20 but at the time it had as much basis as Lane Kiffin to NU, for example.