HENkaku is a native Homebrew Enabler for the PS Vita and PS TV. It lets you run homebrews on the PS Vita
Here is how PC version loads GRP files (expansions or mods that work as campaign replacement):That's something you should check on EDuke32 website i suppose. I don't own Duke Nukem 3D nor original expansion packs so i can't test personally.
This feature is missing in the Vita version. On top of it Vita version can't have different GRP files in the ModDir. If it does all content of those GRP files becomes mixed (with all 3 exapsnion the result is Nuclear Winter intro, Beach sky and weapon textures, normal levels).
Another problem with vita version is the lack of support for "autoload" directory, which in PC version allows to replace midi music with ogg files.