Wispdrinker Vampire's triggered ability checks the power of a creature only at the moment it enters the battlefield. If it enters with counters, those counters are included. If that creature's power is 2 or less when it enters the battlefield but becomes greater than 2 after the ability triggers, each opponent will still lose 1 life and you'll still gain 1 life.

Wispdrinker Vampire's activated ability affects only creatures you control at the time it resolves. Creatures you begin to control later in the turn won't get deathtouch or lifelink.