Well, if it leeches the zinc out, I think it will end up turning them black instead of green. They should also be softer vs. brittle and I'm not so sure that would cause any problems.
I use a tumbler and dump them in there in whatver condition they're in, (after I knock the sand and rocks out), and that Frankford Arsenal stuff with corncob seems to work fast and the corncob lasts a long time, so I'm pretty much satisfied with that combo. Took me about 20 years to come to that conclusion and I tried quite a few things before I did.
I never really did see anything that seemed to hurt the brass any during my experimenting, and I tried a few different chemical solutions, steel wool, 3M pads and different media types. Polish and corncob seems like the easiest/cleanest combo I've found.
I shoot an H-K .308 that makes the cases look like a zebra, covered in soot, so it's a good challange to get them clean.