From the website: http://www.rattyrat.com/guidebook/colors.html
"Rats molt throughout their lives, loosing old hair, and gaining new hair. While they are molting they will have patches of lighter, softer hair throughout their bodies. This is more noticeable in babies. If they have a hairless gene in their background, or if they are a rex, they may even develop bald patches while molting."
So it's possible that rats develop bald patches while molting in certain circumstances.
That's not saying it's due to molting, but it's one possibility. The skin in the pictures doesn't look red or irritated or injured as if the rat was scratching itself. Usually if hair is scratched out the skin is damaged, this is true in most mammals and I deal with dogs doing it on a regular basis.