Well, nobody with any medical knowledge has stepped forward, so…
I’ve seen/heard/read of this and similar things (peeing on your feet, for instance). My own view is: while some (SOME) of the ideas behind them seem to make sense (ie, tannic acid is used to toughen hides to make footwear) there is no evidence aside from anecdotal. Folk wisdom sometimes has some very strong truths to it, but modern medical science (to the best of my knowledge) hasn’t validated any of the ones dealing with toughening the feet.
So, go ahead if you want (I’m not advocating it, but I certainly can’t stop you). The placebo effect may help you out psychologically, if nothing else. I would recommend you seek out some medical advice before you do it, though. I kind of tend to think that soaking your feet may actually be counter-productive, softening up any callus you build. But, I don’t know.
If you do try it, let us know how it turns out. If your feet turn to hamburger, it may prevent others from the same thing. If you find it works, then beauty!