Sounds like a bad idea. More than likely it actually removes brass from the cases, I'm currently waiting for a machine that got Stainless dust in the drive mechanism, it tore up a lot of things in there. Also, it will get everywhere.
Second, you can figure on replacing your tumbler as anything that aggressive will eventually abrade the bottom out of it.
Third, You're going to put dish soap and water where you want gunpowder to work properly ?
Stick with the proven stuff, so what if walnut shells take a little longer, you will be letting them sit for 2 days for the water to dry out.