Probably won't do much of anything if you have a vibrating type tumbler but one that rolls around and around may beat them up some, depending how hard they are. Also there are tails of the rolling style tumblers actually causing a bullet to fire but I doubt it's likely.

IIRC however, it seems that the chemical to polish the brass actually turns the lead dark.

Unless the corrosion is really bad, probably the best thing to do is just move this ammo up in the firing order, shoot it next and then go back to tumbling cases.