I don't know, maybe Colress was supposed to be Dudley but they changed their mind, because of the generic scientist sprite, and it would probably made no sense, to give him a generic one or even a new one.Besides, I'm pretty sure Dudley was more involved with Genesect than Colress (if he was even involved in the project) - he was the only guy who still worked on it.
Dialga and Palkia being in the movies didn't prevent them from having an television role.I doubt Plasma would play a physical role in the movie, considering that they're likely getting their own saga in the animé proper - putting them in a big role in the movie would pretty much be redundant. It's pretty much the same reason why the kami trio are likely never going to get their own movie.
Yeah Dialga and Palkia's role in the Movies were about their rivalry about Time & Space colliding each other and it cause them to hate each other, where it effected Giratina and Giratina's hatred on Dialga and Palkia for nearly destroying it's only home The Reverse World, in their final movie the cause of all this was from Arceus awakening in a rough way that borders Time Space & Anti-matter.Dialga and Palkia being in the movies didn't prevent them from having an television role.
I was solely referring to Plasma having a role in this movie as well as the television series, not the Kami trio.You've got it mixed up - 2 major television roles would make a movie featuring the kamis pretty redundant.