Well they don't have anything as neat as MNSSHP unfortunately! When we were there in October 2003 they did have trick or treating in DTD the Saturday we were there. I wish they would do a hard ticket event since we did MNSSHP last October my family agrees Disneyland needs one too!
Haunted Mansion does a makeover each year for the Nightmare Before Christmas - they do a great job, and this usually opens the first weekend in October.
We are going to Disneyland in October as well, and we have been before during that time and the Haunted Mansion is awesome all decorated for The Nightmare before Christmas. Also, Small World is usually closed to decorate for Christmas.