I have never heard anyone mention that you can, though I really could be wrong. There is Cinderellas Royal Table, Crystal Palace, Liberty Tree Tavern, etc but not sure if they allow wedding receptions. Also you wouldn't be able to wear your dress in the park, unless you were having a MK wedding followed by reception at the castle too.
Maybe someone else will come along that has done it.
Would be lovely. I hope there is somewhere for you.