I can't vouch for all the hotels, but I stayed at the Boardwalk in October 2017, just before Halloween. Did Mickey's Not So Scary Halloween Party and it was fun. Anywho, at the Boardwalk in the lobby, while it wasn't decorated decorated, there was an area where the staff carved pumpkins and Boardwalk Guests were allowed to vote on their favorite.
We were at Port Orleans Riverside the weekend before Halloween and they were decorating for the resort Halloween party. But that was only for the couple of party days. Otherwise the resorts don’t usually decorate for Halloween.