Hatchrite is suppose to have the water already added to the bag, so you pour and go... But I would never trust a company with getting the moisture content just right for every reptile, so if you know what your doing I would add a little bit of water to it, otherwise just pour and go.
Bottom line is yes you need to add water to the incubator for humidity regardless of your substrate choice... You should be shooting for 65%-80% humidity, but the correct moisture content in the substrate from the start will determine how well your eggs develop in the first several weeks, and if mold forms. Just remember the substrate should clump in your hand but should not be ringing wet, the analogy I always use is it should be of "sand castle" consistency but slightly drier...
Best of luck and if you have any questions please don't hesitate to ask!
Anthony