Interesting idea. What none of those articles seems to have mentioned is that sake, and rice wine in general, almost always has acetobacter colonies in it. Perhaps not a huge number of them, but some. You also have a fairly sweet mass of unliquifed rice left. This seems to me to be fairly different then what is left over as trub in western fermentation.
a good thread on the making of saki at home.
Those basic differences would seem to me to pose a bit of a problem for using a yeast cake the way you want to. If you decide to do this, I would recommend adding a small amount of sourdough starter to the yeast cake along with the vegetables. That will introduce the acetobacter that you are going to need for the actual pickling.
In any event, it would make a fascinating experiment. Please post back if you pursue the matter any further.