I think there's an argument to be made that the attraction skews more Christmas than Halloween. Christmas lights and trees strewn throughout, The initial scenes in the Stretching Room recall Christmas card scenes, the Merry/Scary Christmas sign, "We Wish You a Scary Christmas" being sung, Madame Leota's dialogue being based on a variation of "12 Days of Christmas", the Ghost Host's dialogue rhyming in an homage to "T'was the Night Before Christmas," "Ho Ho Ho" and "Merry Xmas" flashing signs in front of the singing busts until recently, Christmas presents and the giant Christmas list, a gingerbread house that changes annually, etc.
These are ultimately all *Christmas* Trappings, and they do not cease to be so because they are being "corrupted" by Halloweentown residents.
The argument could also be made that the default HM is about as Halloween/creepy classic Haunted House as you can get, and thus any addition related to HMH makes the attraction more "Christmasy" as a result.