I have a slight disagreement about your assessment of Summon Vetalas:
This spell gives you 10 Unit #1765 (Possessed Corpse). Not ethereal yet, but not what I would consider fragile. This form has 22HP, 14 Prot, 14 MR, 16 Str, 12 Attack.
When killed they don't die, they are like Onis and they turn into their Vetala form (U#1766). Now they are ethereal, with a brand-spanking new 15 HP and a life drain attack to keep them going.
And the ethereal form heals completely into a new Possessed Corpse before the next battle, pretty much wiping out the "never heals" penalty.
In my opinion, these undead monkeys are serious bad news and I don't think it needs a boost.
(Yeah, I was ravaged by swarms of screaming Vetala hordes in MP, can you tell?
)