I assume that they are more a product of the Blight and the eruption of Red Mountain rather than being products of necromancy. Therefore undead fighting spells and weapons do to have an effect on ash spawn-correct?

Thanks for clarifying.

I think a lot of them is made by Ildari (Neloth supposedly dead apprentice), and I remember Neloth said something about Ash Spawn and Guardians' connection to Heart Stones and their ability to animate and channel magic. So I'm pretty sure they're not undead, just magic animation, like Magnus' anomalies and Ice Wraiths

Or dem Daedras... Since they do a lot of behind-the-scenes shady stuff. I mean, there's no logical reason that magical anomalies would have the faces like baboons on crack? Right??

i think i heard some character (maybe neloth or from his assistants journals) talk about how heart stone rich ash gives the ash the ability to channel souls through it or something
so the ash spawn are some kind of souls/soul residue bound in a body made of ash
so i guess thats kind of undead? still i dont think they can be lumped in with draugr and skeletons

I don't know how the game classifies them, but they do not show up with either detect life or detect dead. They do show up with Aura Whisper.

They are just magical animated objects. Absorb Spells don't work on things that do not live... And yes, Undead does count as living enemies cause really, Undead are creatures that was once dead and now alive.

Basicly, they are similar to Dwarven Machines except with Ash instead of metal.

Try and kill a few with dawn breaker and see if you get the solar flare effect I guess?
I was still using DB when I got to Solstheim but quickly ditched it due to wanting to taste the new weaponry. I set off its effect in the first few dungeons I went through but assuming it was draugr not Ash Spawn.
Would be interesting though, undead with high fire res.

This. I thought they were more of an animated pile of ash than a zombie.