Fill your boots mate. I wouldn't have posted it if I wasn't happy for people to use it.Nice quote, mind if I edit/pinch that for the class...?
Your are quite correct in most of what you are saying. They follow their own sociological and moral construct interdependent of the alignment system, one that rejects the concept of holy (and thus unholy). I would say spiritual guidance instead of "divine"; that might well be a taboo word in this context.If I'm interpreting what you're saying correctly, then the idea of necromancy and undead is only considered evil because of the associations created by the various religions of the world, and the assumption of an alignment restriction on a primal energy (which has always seemed completely off-piste to me too!). Therefore, in a culture which disdains gods and dogmatic principle, using scientific understanding and the 'soul' of their people as their divine guidance instead, the proliferation of undead people throughout society would be more akin to elders and priests than any sort of unholy creature. They're quite the opposite, and I like this.
I imagine that the forces of "evil" created the necromantic lexicon as a kind of negative healing lore as opposed to the divine healing used by the forces of "good", therefore the first generation of spell would have been evil and quite possibly traps. However this society has taken necromancy away from its roots and developed it in ways that the original authors would not have considered or approved off. They could do this because the forces of evil do not have proprietary control over negative energy, despite what it would like everyone to think.
Its kind of like the story of Prometheus stealing fire from the gods. It may lead to a fable/myth of "the one benevolent good" who gave them the hidden secrets of necromancy and was destroyed for it but it may not "jive with the vibe", perhaps the tale of the terrible fate of a mortal messiah as a warning about not letting the gods get their hands on your soul would be a better fit?.
Whilst you might see the occasional one I think that a construct equivalent class would be a much better fit. People who die in this culture are reborn, becoming undead would be a great personal sacrifice -you are giving up your life for the betterment of the people, as such citizens seeking or volunteering for undeath would shoot for a "higher class" of undead. Having said that I can well imagine that a valued serf (say a warden, village elder or serif) could be made into a "corpse" upon death by his vampire lords, particularly if they couldn't or where unwilling to afford one of the more expensive rituals.
I can see a great use for this idea in recycling one of my older concepts. Basically you take one of these "corpses", you lather it in various spell, implanted talismans and enchantments(possibly including a permanent gentle repose), then you (for example) crucify it somewhere as part of a large magical array. Uses might be as a kind of necrotic decanter of endless water as part of a public sanitation or field irrigation system or as part of a beacon network or massive ghost fence.