Are these belly scales? If they aren't it is probably just a bit of retained shed, nothing to worry about.
As long as you keep your enclosure clean and not soaking wet, you should not have to deal with scale rot.
Nope dorsal side scales. I only keep the tubs wet when they are in shed. Example my pastel is in shed (eyes blue) and I mist the paper towel substrate (gets wet fast). Keeps the humidity up to around 80-90% but that is just for the 5 days.