they wont let you in in wedding attire during open hours, the only way you can get photos done is to have a magic kingdom bridal portrait session through DFTW. i believe the current price is $850 and happens either at 5am or 6am.
FYI - You may also be able to do sessions done early in the morning at EPCOT or other parks. Our EPCOT photos were our favorites.
Oh - and I did have my gown on for parts of my wedding reception that were in the parks. We went to the Candlelight Processional as part of the reception (Disney drove us over and escorted us in) and also for the fireworks dessert party. We have some snapshots of those moments.