[Taqwus]

Luck protects against spells, yes -- specifically, the HP damage. It offers no protection against other effects, like being cursed, horror-marked, chilled, set on fire (the resulting HP loss might be protected against, but not the ignition itself, I think), or so forth.

I think it's also the case that it works against Soul Slay -- instant-death spells are actually treated as ~1000 AN damage (which, against -most- things, is instant death; GoH'd in-dominion Sphinxes and heroically obese/tough Tartarians excepted) as can be seen as the damage taken from these spells actually varies. It would not protect against Charm, as that's not hp damage. The same lack-of-protection would hold for stun and paralysis.

My suspicion is that blood vengeance works the same way -- it's probably something checked in a function that deals hit point damage. If it's a check invoked in a hit point damage function, whether or not it came from an AoE effect or enchantment should not matter. One could always create a test map with the Slave to Unreason (who has the highest BV in the unmodded game, AFAIK).