Ferentz has had three OL coaches work under him:
Joe Philbin was the OL coach at Iowa for KF's first 4 years. He was recognized for his coaching ability, moved on to the pros, moved through the GB Packers' coaching staff to eventually become the OC, and is now the head coach of the Miami Dolphins.
Reese Morgan was the OL coach for the next 9 years. He is definitely highly regarding within the coaching industry for his ability. He has never coached outside of Iowa high schools and the University of Iowa, so it seems he is very comfortable in the state and isn't seeking to move on. I think if he wanted to move on, he would have done so instead of moving to coach the DL before last season.
Brian Ferentz is set to enter 2nd year as the OL coach at Iowa. He's only 30 years old, and I think many in Iowa and in the coaching community would agree that he is a guy to watch out for in the coaching industry in the next 20 years or so.
I think Ferentz is a great OL coach, but you're right that he doesn't directly coach them at Iowa. However, he does put a real emphasis on the position and puts great coaches in place to coach that spot.