I can't give advice on Halloween night as I've not been on that night, but I've heard that it's actually relatively light -- probably because so many people are trick or treating, going to parties, etc. We were there last year on November 1st (a Saturday) and it was pretty light. We had pre-purchased Express Passes to navigate the lines, but the park probably would have been doable without them (though the Walking Dead and Halloween houses still had lengthy lines from what I remember). One of the employees noted it was one of the least busy nights they'd had. It was definitely much less busy than when we went early in the week before Halloween in 2012.