Does triggering Guardian Angel reset Darius' Ult?
Solution 1:
The cooldown will not be reset if you trigger a GA passive with it
Technically the champion with GA doesn't get revived. His health stops at 1 (similar to trynda ult) and he is then healed for 30% of their max health after being invulnerable for a short amount of time. You also won't get any other on-kill procs (Varus Passive Attack Speed, Kata/Yi CD resets) if your opponent has GA.
The same rules apply for Zilean ult.