1. First, the millworker had a son. Then the son had a son. This grandson was "born to the son of a millworker." He was not born as the son of a millworker unless his father was a millworker, too. Even then, I would say, he was born the son of a millworker, without the to at all.
2. Well groomed is better. No hyphen necessary when an adverb (well) is the modifier.