Some more suggestions.

1) All nature gems are used to summon carrion priests, so death magic is in fact the main school of CW. I've never been able to cast Mother Oak or even Call of the Wild...

2) Curiously, death magic gives no "national" units to CW, unlike Ctis and Jotun.
IMHO Reanimation, Animate Skel. and Raise Skel. sould give manikins. Animate/Raise Dead should give mandragoras. Undead Horde should give both. Pale Riders sould give carrion cavalry. Carrion Reanimation should give mandragoras (yes that's powerful, but Ench 7 is a long term target for CW). Maybe 10% of stronger carrion beasts, like the undead giants of Jotunheim.

3) The price of carrion priests seems too high and should be slightly reduced IMHO. They are mostly used to reanimate and to cast unholy spells. Nature magic is thematic but practically useless and should not count in their price.
Or give indep priests unholy powers, instead of holy powers (like Ermor IIRC). But who will summon the expensive (in gems) carrion priests then ?
And I suggest to add some death magic to the carrion Lords. They are dead after all. What about, say, 3xUnholy + 2xDeath + 1xNature ? Still in the theme, and not higher than the Apostate.

4) Minor problem : other vine units (vine men/ogre and dark vines) should logically benefit from the special unholy spells.

5) Manikins are good when in large numbers. 3/1 seems a minimum against human HI, and archery fire can decimate them at long range. But autosummoning is very slow, even with a strong dominion. No problem if you control a large empire. Exemple : 20 provinces (including 5 forests) in a strong dominion can give you every turn about 20 manikins + 1 mandragora + 5 carrion beasts (including 1 powerful stuff every 4 turns or so). OTOH 5 Carrion Ladies can give you 2x less manikins but 4x more powerful beasts, even on a small map. So I always give priority to reanimation, over autosummoning.

Cheers