Hi there....it's probably not mouth rot, but if you see inside his mouth, you would look for cheesy stuff on his gums, or some type of inflammation. And yes, you can put unpasteurized [ like from a health food store ] honey on it. It's a natural antibacterial/antibiotic that is good for any wound, including directly in the eye. Just be sure if you use it that there are no loose crickets in the tank since they would bother the beardie by crawling on his mouth for the honey.