I think I have heard of people dressing up as brides at
MNSSHP but usually their policy is no wedding attire. Personally, I wouldn't do it.
You'll make a lot of people really mad. We've had a few posts of people sneaking into MK in wedding attire here and many of the DFTW brides get really upset about it because it seems like cheating. If Disney catches on to what you are doing they have the right to ask you to leave the park and not return and that would be a not-so-fun way to end your wedding day. Plus, you'll likely really ruin your dress if it is a long dress.