Talk about co-incidence. I've been reading the adsense TOS and searching for related topic about multiple adsense accounts on the same page. I couldn’t find any definitive explanation. Luckily, Adsense has just released an explanation on it on their official blog that clarified the issue. I can't simply copy what digitalforum is doing since they are premium adsense publishers.
You see, I'm about to launch a site with my friends that will allow members to show their ads on their submitted articles. It's some kind of revenue sharing but instead of splitting the proceeds, the members will get the full revenue of generated on their ad units displayed on their article. A separate ad unit, this time for the site, will be displayed somewhere else in the page. Revenue of this ad unit will be used for the upkeep of the site. It will generally make less money since the user's ad unit will be the one to be embedded on the article.
That's where the problem comes in. Though it's clear that a site can show multiple adsense publishers, doing the same in a single page isn't clear. And just about when I was going to contact adsense support, I visited their site and found their announcement. It's not just me having this problem afterall. And with this clarification we can go ahead with the development and eventual launch of the site.
The full text of the clarification can be found at the link blow.