Shooting zombies and costumes is a blast. I always shoot them off-color and at a little slower shutter speed for that blurry "I'm going to get you" feeling. Don't forget to hold the camera a little off center and rotated a little, to really give the viewer that off-balance scary feeling.
I created a group of "Zombie" Lightroom Presets to make editing faster. Feel free to check them out! Provided free from 24Moves.com and HoustonPhotowalks.com