With the default action "Add files to playlist", you can only add music files to iTunes. There is no way to make an Automator workflow that would add videos directly to iTunes.

It seemed to exist before, but apparently it’s not any more in the iTunes default actions and it’s annoying.

The AddMediaToPlaylist Automator action provides a more generic step for your workflow that will work with videos. Just select the playlist you want the files to be added to and it will do it for you. AddMediaToPlaylist can also create the playlist if nee

Installation: Download the Automator action. You can either select "Import Action..." from the "File" Menu in Automator and choose the action file or manually move the action file to the Home > Library > Automator folder.