They've been working together on and off for 17 years. I'd say that is far more than just familiar, especially when Loomis has the ability to sever the relationship whenever he chooses. Instead he chose to bring him back after his stint in Denver and Oakland and keep him on after Payton left. That indicates that they at the very least have a very friendly working relationship, but I suppose it doesn't mean they go bowling together on Tuesday night during the off season.