Not sure what all the worry about foreign wort is. If I can get a 42 from 3 grand master judges on a Munich Helles using foreign wort, I'm convinced it's not a concern.
Just make sure your starter wort is at or below target fermentation temp before you add your oxygen and yeast, and that it's active when you pitch it to the main beer.
That temp part is the one thing I'm still thinking over. Normally when I repitch, the yeast is colder as it's been in the fermentation fridge near freezing as the fermenter makes it from ~60°F (wort chiller) to 50°F (pitch.) That seems too cold to get it active, as would be the lagering freezer (29°F) or keezer (38°-40°F.) Room temp it would get active, then be knocked out at pitching. I still have some things to work out before this is a sure option for me, till then I'll repitch 3-4 day old slurry. But Denny' s convinced me not to bother rinsing.
One thing I like about the vitality idea for a lager is, it is in principle a lot like Darauflassen. Same goal, keeping yeast in the growth phase as long as possible, and similar method. Just that the two worts are in different proportions.
EDIT Other thing I don't like about foreign wort, not that it's foreign, I just don't want to bother making a separate dme wort. I'm not a guy who cans a year's worth of it, because I only make a starter once a year or so!