Cool mist humidifiers don’t pour out cooled mist; it’s simply room temperature water. If you’re in direct contact with this, it will cool you down as the water will be at a much lower temperature than our bodies. In terms of the overall room temperature, it will have a negligible difference.
You would be able to pair them with heaters in most cases, but this isn’t something you should do without checking the manual. It's always important to check what the manufacturer says about that first, and if you’re unsure, ask a question about the specific model to be able to get the answer you need.