It has been confirmed that Captain Gantu is not in the live-action Lilo & Stitch. While he is not a major part of the original animated film, he does serve as the main villain who sends Pleakley and Jumba after Stitch. I cannot imagine that Disney made this decision lightly, so hopefully it does not mess with the plot or flow of the film too much. I imagine they just give a little more to do to either Pleakley or Jumba (likely Jumba). Initial reactions by those who have seen the film alredy are mostly positive, so I am not too concerned.