Yes, that is true they cannot be grown in the tank - they need the vinegar.
Here is the info, they are so tiny I can barely see them, use a slice of apple and Braggs apple cider vinegar in the jar.
The hang on the back or fuge type things return water back into the tank, so I can not think of a worm or creature type food to raise in the back. Other than maybe common Cherry shrimp.
Which you would need so many to actually feed the fish. Breeding in that small of a space wouldn't be able to produce enough babies for daily feedings.