not a DVDit user but the way this would work into DVDSP would be at the end of a slide show jump to a video track, then jump to another slide show after that track ends. Hence the appearance of a single slide show with a video in the middle.
And that is how you would do it in DVDit Pro. Create slideshow 1 with 10 slides. Set the end action for the slideshow to the movie clip. set the end action for the movie to slideshow 2. You also have access to playlists where you can make this possible. So, alternatively so could place slideshow 1 into a playlist and movie 1 right after it and then slideshow 2 right after that. That way you can have a different playback order for the same assets that you are linking to from your menus in some other fashion.