Ok, lets all reset for a second. It's BHG's Wife who thinks the getting Anya pregnant is immoral. We're all being left to speculate on what could cause her to think that all without knowing a thing about the woman, and so we're focusing on in game. I'll mention an example as I recognize many people here from other games, many of us here play incest games. Incest, even just in games, is still seen as immoral and incestuous pregnancies even more so, regardless of the consent or willingness of the parties involved. Say Mrs BHG is against incest, she deems it immoral fictional or otherwise, many of us here would disagree. So getting Anya pregnant could be a similar situation, or it might be that we'll stop and go "No, she was right. Getting Anya pregnant like this would be fucked up".
That said, yes part of the problem with necrophilia has been and is the lack of consent thing, it's also been seen as defiling/disrespecting the corpse. Not to mention the influence of various religions.
Not to start a fight again, but I don't count sentient undead as actually dead and thus not as necrophilia.