yea pretty much , here's the deal the vinegar is simply to speed up the process of reducing the iron(rusting it away) and putting it in a liquid suspension . You could use plain water but it would take much longer than the vinegar. It doesn't have to be exact in any way and its about as sciency as putting a mento in diet pop.
If you use stronger vinegar then you also put stronger acids on your leather which isn't good, neither would be the oil you wanted to put on top of the mixture to keep out air. Remember the end result is to produce a liquid you can put on leather, dye it black, and not ruin it.
There are more than a couple of threads on this topic it may be good to read through some of them, there are also other ways to make the roon.
Good luck!!!