Sorry I'm don't know enough to identify that either. Is it just a white spot, or is it a bump that protrudes out some? I can't tell from the pics if it has a soft fuzzy texture/coating or is it smooth like it's showing through from under the skin?
I wouldn't think Melafix would hurt it. Even if's not something that will treat whatever that is, I think it would help with your Convict's overall healing and recovery in general.