Can you list off people's names and see what her reaction is? So you are not singling people out.
I don't think it would be a good idea to name off this persons name when having this conversation, as we don't want it going back to him that this topic was being discussed with her and his name anywhere near it.
Beyond anything we want to deal with as this is a parental figure who we have to do drop-offs and pick-ups with. With-out any solid evidence we don't want to make this person think we are putting in her mind that this is a bad person, because that is not the goal. The goal is simply to make her aware of what is acceptable, unacceptable behavior of people around her, including people that she may trust. Stressing - people that she may trust - not just "strangers".