Apparently not... at least none I can fine for picture slide shows. You can with regular DVD's, I do that all the time.
A simple work around is first determine the length of your slide show down to the second. Then render whatever songs or songs you want as a background as a MP3 in Vegas. Next load all the images you wish in the slide show in the right pane and at the very bottom locate the song or songs you made into one track using the explorer. Just click on the folder icon under background audio
There's also the Looped box on the page properties tab, right side window. Applies to the BAckground audio file.
Haven;t gotten a truly smooth loop as it gaps at the end of every go 'round. But it does save media space and gives a loop. Would be better if it was seamless - v2?