We went through the same dilemma - we wanted a kick butt ceremony and reception in the park, but we wanted outside photography. We ultimately decided that we'd rather have the pictures than the location. (And in the grand scheme of things, it's saving us money!) Sometimes I feel like we're having a cookie-cutter Disney wedding (WP/Attic/UK DP), but I remind myself that no one attending will realize that - it will be so out of the norm for them.
With that said, the photographers will not risk their working relationship with Disney for some shots in the park for a random couple. Every wedding they photograph on property, they sign a waiver/liability/rules/release type form. If they are found to be breaking those rules, they run the chance of not being able to shoot another wedding on property.
We, too, asked if they would be willing to take a few pictures at our dessert party if we included them as guests and the answer was a polite, but firm, "NO." Even if they wanted to, they are around the parks enough to be recognized and don't want to run that risk.
I truly feel your pain, but you'll have to decide whether the ceremony/reception locations or photography mean the most for you and then go from there. And, as others have said, you can have some great engagement shoot photos at any of the resorts!