He cant be hired in an OFF field role is the rule. See below:
Going forward, an FBS school can hire a high school coach as one its 10 on-field coaches, but cannot add one to its support staff - which is a critical professional stepping stone – unless the college has not recruited one of the high school coach’s players in the past two years. And if the college does hire the high school coach, the college then cannot recruit a player from the coach’s former high school for two years, making it essentially a four-year window, two years in each direction.