I tumbled (vibrator type) some bullet years ago to remove the case lube, but they were all jacketed. The two thing I noticed from that were the accuracy of a known load went to pot, and the lead tips on the Partitions were pretty deformed. I cannot say that the actual powder was damaged during this or that the tip being deformed changed everything as I have shot the same bullets with the tips knocked all sorts of ways and never got out of MOA out to 200yds. These particular loads wouldn't keep that at 50.
FOr lead bullets, if I am wanting to clean the cases I do so before loading, if I am simply wanting the bullet lube off of them I just sit down in front of the tube with a rag and some denatured alcohol and wipe them off.
Most of the time I clean my brass in batches of 3-500 and then load them all up. After that I don't sweat how they look and with the cast, I don't sweat the lube unless I am loading for hunting, and even then I don't worry too much about it. Wiping it off DOES help keep the accumulated dust and grit down to a minimum however.
Mike / TX