lately, a large portion of my income has come from shooting weddings (not my fav. but it pays and you meet a lot of people, lol) i would FIRST make sure it is okay with the bride, not just okay, but that she actually supports it. THEN talk to the hired photog. theres nothing i stand more than reviewing my files for the group shots and seeing family members looking in other directions because some uncle with a DSLR is right above my head saying "smillleeee, look here". i mean im getting paid for it, so dont interfere on my work. im sure the photog would be okay with it as its a sort of nostalgic thing with the huge 4x5. i would not take more than 5 photographs though, depending on how fast you can get through them.