The Frightfully Fun Parade, along with the Headless Horseman, are listed on the website under event highlights, so baring technical difficulties, they should be presented!
What is the Calaveras attraction?
It depends on whether you have flexibility in your schedule and what dates specifically you were thinking of going. If you have the choice between a Friday and a Saturday, I would opt for the Saturday because DL will be open late and there should be nighttime entertainment (e.g., fireworks, F!, etc.). In general, if you aren't planning on going to the party, I would probably opt to go to the parks on a non-party day just because you don't have to contend with the earlier closing and the potential uptick in crowds during the overlap period.
Park hours can vary, but wdwinfo has the historic hours from
September and
October 2017 posted. It seems like DCA closed at 8:00 pm on most weeknight days last year in October, regardless of whether there was a MHP or not. DL "closed" to non-party guests at 6:00 pm, the start time of the Tuesday parties.