I keep on hearing how google bans all sites asociated with a banned account... so would that mean there is a risk in your site getting banned if it displayed ads of a banned accout?
I doubt if they will ban DP if there are one or two people here with banned accounts sharing in its shared program.
mate, I'd contact them first, notifying them that if ever there was a banned account being used on your site, it is due to your site/forum being a revenue sharing forum, and so people may be using banned accounts, and ask them to contact you to remove the banned publisher if it ever occurs... The Google AdSense team are usually quite reasonable if you ask first.