I think we are getting bogged down in the details and missing the big picture.
The big picture is UK football and the fact that it needs help.
Sure, plenty of coaches wouldn't be interested in coming in to be actual assistants/coordinators or contributing on some sort of advisory committee.
But there are coaches who would be interested, and getting guys to come in and help is exactly what winning programs do. It's also not absolutely a must that top tier winning coaches be brought in.
See Joker Phillips. Urban Meyer brought him on to be "quality control". The title isn't important, what is important is that Ohio State football and urban recognize the value of having somebody like joker come in. Yeah he failed miserably as HC, but he was at one point a highly thought of OC and does have experience in P5.
What is one thing Urban needs to concern himself with? SEC recruiting, and SEC opponents in the play offs. Urban has plenty of experience with that himself, but Joker gives him some fresh eyes.
Look at Saban. He brings in a dumpster fire in Sark. No body was going to touch that guy for at least a little bit, he was going to have to go the juco/high school ranks, or to the booth. Saban said no, I'll take a HC with P5 experience and offensive mind, an ace recruiter and I'll make him an "offensive assistant".
Saban is not only thinking that it will be an extra guy for x's and o's, but it's a guy who knows the pac 12.
Sark may know about a couple Cali recruits he was looking at while at USC. Saban may have to game plan for Washington in the play offs.
That is how and why programs win, whether it's Toledo, Bowling Greene, Utah, MSU, LSU, Bama, Florida, or Ohio State. Thinking like the above mentioned coaches is why they are two of the very best in the game.