LaVell was a DC prior to being BYU's head coach. So did Kilani.
But I cannot find a time in recent BYU history where the OC has had ZERO prior D1 experience:
Scoville had experience (QB coach).
Holmgren had experience (OC)
Norm Chow (WR/QB)
Gary Growton (HC)
Robert Anae (1992-2004 OL)
Brandon Doman (05-10 QB)
Ted Tollner (was SDSU OC, came as lowly BYU QB coach)