I was on the Halloween cruise last year. If you decide to go then definetly bring costumes and get in touch with the other Halloween cruisers here. They have some awesome things planned including one of the best trick or treats that I have ever been on! You will LOVE the Halloween cruise.
As far as what disney does: They offer their own trick or treat which I here was very fun, although I myself did not attend. If you have any teens going please be sure to let those on the Halloween thread know, one of my friends would love to have someone to hang out with.