Only spiritually - the body Polly is in now is not the one Ares sired, and as far as we know doesn't even look similar or have more than the most hazy memories of an existence prior to her recreation by the Patrons - and anyway, as cmdr_zoom says, he's an Olympian. His own mother is also his aunt, and his lover and the mother of his child is (variably) his sister, it's not like incest is a huge obstacle for him.