From a 'person with 20/20 vision' point of view, I would say, hell no.
I have nothing against the man, nothing at all...however, when someone has a forehead so big that you could screen 'How The West Was Won' on it...well, you can see where I'm going here.
I think some of his features like his smile are like James Hewitt's too apart from his hair. But hey Charlie has brought him up so he is his father anyway regardless.
He is nice looking too and like you I would say not my type but can appreciate their looks.
I think Harry is just like his Uncle though (Charlie Althrop) so for me, that blows the theory away that he's the love child of James Hewitt. I dont think she was even seeing him at the time Harry was concieved was she, correct me if im wrong.