This may or may not have occurred to you, but what if he doesn't care? What if he doesn't mind whom she brings home at Thanksgiving? What if he is just happy that she is happy? Does he need the approval of FReepers on what he thinks of his daughter?
If he doesn't care (and I am not speaking for him, but am parroting your words) then he is not (in my book) a good Republican.
One's personal familial circumstances cannot dictate one's core principals.