Did Zack have any lines in Final Fantasy VII: Advent Children?
Considering Zack has his voice actor listed in the original Final Fantasy VII: Advent Children's credit... yes, he spoke 2 lines near the ending.

This happens after Cloud's final fight


   when Cloud is unconscious after the Remnants of Sephiroth's suicide attack. After a while, Aerith and Zack have a very short dialogue, rejecting Cloud's fate from "joining" them.
  
  
  YouTube video: Japanese voice, English dub.




With the additional screen time for Zack in Final Fantasy VII: Advent Children Complete, he also has more lines compared to the original movie.