when my brother got married, no boyfriends or husbands were allowed in photos, it was just family. We had photos taken away from the main wedding party or informal pictures. So I agree!If
he doesn't and she's "fine" about it we will know that the final death nail of her self esteem has been hammered in.
In all seriousness those wedding photos will (hopefully) be forever, so if i was her sister i wouldn't want a rando (even a mildly famous) one in my wedding album. He probably should be in any of the offical photos, but absolutely should be her plus one. (Imo)
however I wouldn’t be too surprised if her sister said no, I wouldn’t want my sister’s boyfriend of 2 years who was a “celebrity” at my low key wedding!