Vob passthrough only have a option to write a separate subtitles. The final files are IDX and SUB. SUB are a set of subtitles in bitmap format like DVD store in VOB. IDX are a text file with the instructions where each subtitle is on SUB file.
This idx/sub format can be read from almost all media players (media player classic, VLC and others). And you can install a directshow filter named dvdvobsub to see the subs with any media player that uses directshow.
The problem is almost all DVDs I have ripped can't be read from dvdvobsub and avisynth filters like VSFilter. I need to rip the subtitles again using VSRip (the best method to rip subtitles in idx/sub format and DVD Fab can't beat since the creation). Sometimes I need to post a new thread here to resolve the problems with subtitles but some versions after the problem return.