I don't know who you talked to, but i have had either gmac or on of their subsidiaries insure all my busses since 1989, and i have never had to have an appraisal, or photos. I would suspect that you either had the wrong sales rep, or you told them you have a school bus, and want to convert it or something like that..I have always partially converted my 5 busses and then called them, and have never had any problem. I now insure all my vehicles (except stree rods) with gmac.
maybe you could call and just talk to a different person...