It is known that Paladins can heal themselves with a Swift Action:
Lay On Hands (Su)
Beginning at 2nd level, a paladin can heal wounds (her own or those of
others) by touch. Each day she can use this ability a number of times
equal to 1/2 her paladin level plus her Charisma modifier. With one
use of this ability, a paladin can heal 1d6 hit points of damage for
every two paladin levels she possesses. Using this ability is a
standard action, unless the paladin targets herself, in which case it
is a swift action. Despite the name of this ability, a paladin only
needs one free hand to use this ability.Alternatively, a paladin can use this healing power to deal damage to
undead creatures, dealing 1d6 points of damage for every two levels
the paladin possesses. Using lay on hands in this way requires a
successful melee touch attack and doesn't provoke an attack of
opportunity. Undead do not receive a saving throw against this damage.
Could a Dhampir Antipaladin cast Touch of Corruption to 'heal' himself with a Swift Action as well? And if there is not rules-as-written for this, would it be fair?
Touch of Corruption (Su)
Beginning at 2nd level, an antipaladin surrounds his hand with a
fiendish flame, causing terrible wounds to open on those he touches.
Each day he can use this ability a number of times equal to 1/2 his
antipaladin level + his Charisma modifier. As a touch attack, an
antipaladin can cause 1d6 points of damage for every two antipaladin
levels he possesses. Using this ability is a standard action that does
not provoke attacks of opportunity.Alternatively, an antipaladin can use this power to heal undead
creatures, restoring 1d6 hit points for every two levels the
antipaladin possesses. This ability is modified by any feat, spell, or
effect that specifically works with the lay on hands paladin class
feature. For example, the Extra Lay On Hands feat grants an
antipaladin 2 additional uses of the touch of corruption class
feature.
Best Answer
A dhampir antipaladin takes a standard action to use touch of corruption, but there's more to it than that
There are, in fact, several issues with a dhampir trying to use the antipaladin's supernatural ability touch of corruption to heal himself:
(Just in case the d20PFSRD failed to mention that touch of corruption really is negative energy, I checked Paizo's own SRD and neither is touch of corruption mentioned there as being negative energy, nor is it said to be such in its original form on page 120 of the Advanced Player's Guide.)
That's a fair number of house rules a GM must make if the antipaladin's supernatural ability touch of corruption is to function the way I expect you want it to. For comparison, the FAQ says the paladin's supernatural ability lay on hands as uses positive energy, but there's no corresponding FAQ entry saying the touch of corruption uses negative energy. While I understand the desire for the antipaladin to be the equal and opposite of the paladin, that doesn't seem to hold true in this case
"Would it be unfair to allow a dhampir antipaladin to take a swift action to use touch of corruption to heal himself?"
Maybe. If my PC were a paladin (or another PC with lay on hands) in the campaign, and if the campaign weren't undead-heavy, making only the above change but otherwise playing everything else as written allows another player's dhampir antipaladin to heal himself and battle with greater efficacy most foes better than my PC paladin who, unless battling a rare undead foe, can only heal himself. So, yeah, I would see that as a little unfair. In fact, I'd maybe have my paladin steadily become more and more bitter and sullen until he finally sought out someone who could offer him a deal that would even things out between my PC and his ally, even if it meant that, technically, my PC wouldn't be, y'know, alive anymore… I mean, undeath sounds unappetizing, but unlife? That's just like immortality but with a slightly different flavor, right…? And all that juicy power…?
Anyway, absent another PC in the party with the supernatural ability lay on hands, making the above change to the supernatural ability touch of corruption probably really won't matter to anyone but the dhampir antipaladin, but a GM should be prepared to make similar changes to other classes if it does end up mattering, just in case. Seriously, there's no way for me to really know what anybody else's group thinks is fair.