You can touch a pad with almost all of your back sleeping on the ground as well, it depends on the pad and how much cushioning it has. In my experience a pad does not have to be sweat producing. You need to use some wicking material with some of them, vent on the top side as necessary, and not try to use them in a hammock when it is just too warm to need insulation.
When I am using a breathable underquilt, I will sometimes use a silnylon or plastic sheet between it and the hammock as a vapor barrier when the temperature drops to extend its lower temperature range. In general, you would prefer your insulation to be more breathable when you are using it near its upper temperature range and less breathable when you are using it near its lower temperature range. When you are overheating, breathable insulation helps deal with sweating. When you have a vapor barrier you stop producing insensible perspiration and because of that you can be comfortable at lower temperatures with the same amount of insulation.