Is it safe to use a heating pad on an inflamed stomach?

Inflamed stomach?: No idea what inflamed stomach is. Yes, especially if you have cramps heat can help. Watch not to burn yourself however. Also would be advisable to check out with a physician your symptoms. Heating pad is just for a symptom, find out why you have them...

Generally yes: Never on high heat! or while sleeping! one can get burned. If it is comfortable it is unlikely to be harmful anywhere. ( except diabetic, or neuropathic feet where real damage can occur since the feeling is diminished or absent).