Are you interested specifically in the Magic Kingdom? Because people have after-hours weddings inside Epcot, Animal Kingdom and Disney's Hollywood Studios all the time. There should be numerous planning journals and trip reports in the "Planning Our Happily Ever After" subforum of this board. I have interviewed many of these brides on my two podcasts.
The Magic Kingdom is not open to evening after-hours wedding ceremonies and receptions due to restrictions placed by park management and a lack of catering facilities within the park. However you can get married there if you have an early-morning ceremony that starts before the park opens. I have a on that too!