Here's what we know:
* He is a Death Eater: Zabini's allegiance to Voldemort is confirmed in the books. He's seen participating in Death Eater meetings and attacks.
* He's present at the Battle: He is present in the Great Hall during the Battle of Hogwarts, as seen in *Harry Potter and the Deathly Hallows*.
* His actions are not detailed: The books don't specify if he actually fought or what role he played in the battle.
It's likely that he fought in some capacity, considering his allegiance and presence. However, his role in the battle is never explicitly detailed.