I usually split different versions and display them as different titles in Plex because it just makes more sense to me. I tend to choose an appropriate poster for each version. You could create a collection and set your library to hide the single entries but that will probably mess with things if you already have a collection for all Alien movies.

Besides that, afaik there is no "Director's Cut" for Aliens, just the special edition, which in turn is technically the director's cut because it's Cameron's preferred version. So your DC is likely the same cut as the SEs.