Does immunity to damage render a creature immune to the other effects the damage could cause?

Question

A shifter (Races of Eberron 25–40), in addition to the feats Endurance (Player's Handbook 93) and Toughness (101), takes the feats Shifter Stamina (115–16) and Troll Blooded (Dragon #319 61).¹

The extraordinary ability regeneration 1 that's granted by the feat Troll Blooded causes the shifter to be dealt—all the time—nonlethal damage except by effects that deal acid or fire damage. The feat Shifter Stamina renders the shifter—while shifting—immune to nonlethal damage. Hence, while shifting, unless an effect deals acid damage or fire damage, for the shifter, the effect deals no damage.

However, I'm unsure if this also renders that shifting shifter immune to any ancillary effects of a damage-dealing effect, like a poison were the poison to have been delivered by a normal weapon attack or the ability damage that would've been dealt by the rogue's special ability crippling strike (PH 51).²

Is this immunity to damage defender-facing, as in That effect dealt me no damage therefore I ignore all of its effects completely? Or is this immunity to damage attacker-facing, as in O, I totally dealt damage with the effect, but the enemy to whom I dealt it just so happened to be immune to it? Or some combination of both? Or is there another—I hope easier!—way of adjudicating this combination of abilities?

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¹ The Troll Blooded feat's regional type requirements can be met with 2 ranks in the appropriate Knowledge skill. Greyhawk regional feats have rules for later-than-level-1 acquisition similar to how Forgotten Realms regional feats functioned when originally introduced in the Forgotten Realms Campaign Setting. While how Forgotten Realms feats could be acquired was changed by the Player's Guide to Faerûn, nothing changed how Greyhawk regional feats can be acquired.
² For comparison, the Dungeon Master's Guide glossary on damage reduction, in part, says, "Whenever damage reduction completely negates the damage from an attack, it also negates most special effects that accompany the attack, such as injury type poison, a monk’s stunning, and injury type disease" (292). To be clear, a similar note is absent from any description of the regeneration ability.

Answer 1

I would apply this damage reduction rule here:

Whenever damage reduction completely negates the damage from an attack, it also negates most special effects that accompany the attack, such as injury type poison, a monk’s stunning, and injury type disease. Damage reduction does not negate touch attacks, energy damage dealt along with an attack, or energy drains. Nor does it affect poisons or diseases delivered by inhalation, ingestion, or contact.

^{(Damage Reduction special ability description)}

Obviously, immunity is not exactly the same as damage reduction—it covers non-physical damage as well, and in any event doesn’t describe itself as “infinite damage reduction” or any such thing, but this is probably the clearest wording we have available. After all, we are talking about an attack that hit, but failed to deal any damage—whether it was due to damage reduction or immunity seems a bit besides the point that no damage was done. Certainly the reasoning on offer here would apply equally well to immunity.

But of course, regeneration isn’t truly immunity—it’s damage conversion, from lethal damage to nonlethal damage. Then Shifter Stamina is making you immune to the nonlethal damage. But, and this is the important bit, damage never gets done. At no point would it apply to the character (as opposed to the usual case with regeneration, where it applies but is soon healed). Consider: would an attack that was already nonlethal, applied to someone with Shifter Stamina (and possibly not Troll-Blooded), apply such rider effects? I wouldn’t think so—though admittedly the rules are silent on that particular case, it just seems inconsistent for damage reduction to negate those effects but immunity to not do so. And then with Troll-Blooded, you are taking nonlethal damage (from non-acid, non-fire damage), so Shifter Stamina applies and you again take no damage.

Note that the definition of injury poisons repeats this statement, but also describes the poison overall as requiring, well, an injury in order to dose the target. While what, exactly, hp is an abstraction for is nebulous, it’s probably reasonable to assume that in all cases where 0 hp is lost, no injury occurred.