I went to 1900 Park Fare last December and none of the characters were in Christmas attire. Alice was dressed in her winter outfit with long sleeves insteed of puffy sleves as usual, but I'm sure it was more out of practicality than festive attire since it was pretty cold that day.
I know in the bast that the characters at Donald's dress in Christmas outfits and that sometimes characters may wear Christmas adornments on Christmas day (I know I've seen some pics of the Princesses at CRT with holly in their hair on Christmas).