Hang on ...
In these circumstances, a VSO PhotoDVD slideshow would be a complete
VOB set and ifo/bup files ... A movie "DVD" not a "file"!
How can these be ADDED to a conversion as another title?
And if they are, would not the VOB set be re-rendered with resulting loss of detail?
Never tried this!

Can you add a completeDVD set as another title?
Peace ... Bags.