The subject is immune to all death spells, magical death effects, energy drain, and any negative energy effects.
...
TOUCH OF TAINT [MONSTROUS]
One of your attack forms that normally deals ability damage, ability drain, or energy drain can also deal corruption or depravity.
Prerequisites: Natural attack that deals ability damage (including poison), ability drain, or energy drain.
Benefit: Choose one of your natural attacks that deals ability damage or ability drain or bestows negative levels. That attack now increases the target’s corruption or depravity score by 1 point along with the ability damage or drain it deals. If your attack deals ability damage or drain to a physical ability score (Strength, Dexterity, or Constitution), it now also increases the target’s corruption score. If the attack deals ability damage or drain to a mental ability score (Intelligence, Wisdom, or Charisma), it now also increases the target’s depravity score. If the attack bestows negative levels, you can choose whether it increases a specific target’s corruption or depravity score.
If the attack you choose bestows more than one negative level, it now increases the target’s taint score by 2 points. You can choose to have it increase a target’s corruption by 2 points, increase a target’s depravity by 2 points, or increase each score by 1 point.
If a Vampire hits a target with a slam attack, and that target is protected by
Death Ward, is he also immune to the taint increase? He didn't take the negative level, after all.
What about a Warforged character, who by their very nature (living construct) are immune to energy drain?
Unrelated to Touch of Taint, but related to Death Ward and Warforged, what about the Fell Drain metamagic feat?
FELL DRAIN [METAMAGIC]
Living foes damaged by your spell also gain a negative level.
Benefit: You can alter a spell that deals damage to foes so that any living creature that is dealt damage also gains a negative level. If the subject has at least as many negative levels as Hit Dice, it dies. Assuming the subject survives, the negative level disappears (without requiring a Fortitude save) after a number of hours equal to your caster level (maximum 15). A fell draining spell uses up a spell slot two levels higher than the spell’s actual level.
I guess the Warforged question hinges partly on if Living Constructs are "living creatures," which I would argue they are.
But Fell Drain isn't technically Energy Drain, so I don't think Warforged are immune to it that way.
Edit:
Dredging through the google cache of WotC message boards, I found a similar question (Fell Drain vs. Warforged), and this seemingly excellent answer by Tempest Stormwind:
There are other ways to apply negative levels that are not connected to necromancy at all - if the Lord of Blades (an Evil warforged juggernaut) were to pick up a Holy sword, he'd suffer negative levels, for instance. Warforged juggernauts aren't immune to negative levels.
Furthermore, there are many things that aren't Necromancy nor [Death] effects that apply negative levels - the Death Devotion feat, for instance, or, yes, Fell Drain (if applied to a spell from a school other than Necromancy, and a spell without the [Death] descriptor). These bypass the warforged juggernaut immunity.
By the rules, I believe the player is in the right here.