It is perfectly fine to use both a heating pad and lamp as long as one or both are controlled by a reliable thermostat. Heat lamps and bulbs do tend to suck the humidity right out of the tank though, so misting or placing the lamp above the water bowl should help a bit. I would try covering a 1/4 to 1/2 the top of the enclousure with a damp towel or cloth to help lock in the moisture. Also adding some damp sphagnum moss or paper towel to one of its hides can help with humidity alot and give your animal the option to choose the humid hide or non humid hide. The Ball Python knows what it needs, you just need to provide it for him.