I have had this experience at my own wedding, when my friends and family members brought out their point-and-shoots and mobile phones during the formal poses. As a result, many of my immediate family members were looking in a different direction. I was pretty busy and ill on that day, so I didn't notice it right away, nor did the hired gun say anything. But I was very annoyed afterwards- if he had informed me what was going on, I'd have asked my family members to pose for the photographer irrespective of who else was shooting.
At the end of the day- it is the hired photographer's responsibility to get the job done. That includes dealing with insensitive guests, impatient brides and grooms, finding workarounds, and everything that entails. Befriend, request, coerce, force, blackmail, threaten- do whatever you need to, but get the pictures.