Colm Meaney is not that big a movie star, and we're talking about little more than a cameo appearance. Meaney seems a good guy and one who was always willing to do what the producers asked of him, such as appearing in the TNG finale. I can't imagine he would have held them up for some huge some of money for a day or two's work on the movie.
Colm Meaney is probably the most successful "character actor" from any of the 24th century Trek shows, when it comes to getting continous work in movies. I was surprised that he wasn't in First Contact, but for all we know, he may have been busy working on a movie at the time, and wasn't available. Still, a shame he wasn't in the film.