As long as anyone who is displaying ads on a page has permission to display ads on that page, there should be no problems. It is even possible/acceptable to have different publishers with ads on the same domain (not including subdomains)...or so I believe based on reading the TOS.
Hmm.... thanks! That seems to lead me to more questions then.
Let's say that you have a site and 5 publishers are publishing on that domain in their own subdomain area and then the main domain.... www.yourdomain.com gets their account banned. Would everyone else get their account banned or just can't show ads on that domain.
In addition, what if it's reversed. www.mary.yourdomain.com gets her account taken away. will everyone lose their account including the main person because mary got banned?
Regarding the banning, only Google can answer that one with certainty, but what I read leads me to believe that the banning is on an account and on a domain basis so yes.... you are probably risking the whole domain.