Bloodlord of Vaasgoth plus Warstorm Surge, then casting a vampire creature spell
This is incorrect; the damage will be dealt too late for Bloodthirst.

You were right up to a point... but Warstorm Surge triggers on a creature entering the battlefield, meaning that it will not trigger until after Vampire Nighthawk is on the battlefield, completely done resolving.

Note that Bloodthirst creates a replacement effect, that changes how a creature enters the battlefield. It does not do anything once the creature is on the battlefield.

The actual order of events, assuming that both players pass priority when they can.


Cast Vampire Nighthawk.
Bloodlord of Vaasgoth's ability triggers.
Bloodlord of Vaasgoth's ability resolves, giving Nighthawk Bloodthirst.
Vampire Nighthawk resolves; entering the battlefield - its bloodthirst doesn't do anything because an opponent was not dealt damage.
Warstorm Surge triggers.
Warstorm Surge resolves, dealing 2 damage to your opponent (or any target).


Bloodthirst rules:


  702.53a Bloodthirst is a static ability. "Bloodthirst N" means "If an opponent was dealt damage this turn, this permanent enters the battlefield with N +1/+1 counters on it."


We know this is a replacement effect because of:


  614.1c Effects that read "[This permanent] enters the battlefield with . . . ," "As [this permanent] enters the battlefield . . . ," or "[This permanent] enters the battlefield as . . . " are replacement effects.


To do what you want, Bloodthirst would need to be a triggered ability instead of a replacement effect; and it would also have to be worded in such a way as to avoid having an intervening if clause so that the condition would only be checked when it resolves (rule 603.4).