When Jimmy got to Michigan one of the first things, he did was bring in valuable staff members to help run his football program. These resources are not officially on-field coaches but do things like scout opponents, prepare nutritional menus, book travel, academic help, help with game planning, etc. Yes, some are former coaches and some of these resources have gone on to head coaching jobs. Biff Poggi is a great example of that.
This is very common place at any big college program. Alabama for the longest time was doing it better than anyone and was winning a ton of football games.