Just sent an email to BBS asking. I also found this thread from an E46 guy quoting BBS on forged wheels. It's not a "first-hand" source but have no reason to NOT take him at his word that he spoke with BBS.
http://forum.e46fanatics.com/showthread.php?t=767096
Pershaps the powdercoating concern is with forged wheels and not cast ones like ours??? Anyway, I will post the result when I get it.