Keeping aside the factor of duplicate accounts, technically there is nothing wrong using two different adsense accounts on same website. I have seen many forums/article websites offering revenue sharing services by letting their members to add their adsense publisher ID. However, it should not be two different pub IDs on same webpage.
I didnt find any issues with different PUB Ids on the same page, it will not make problem. Some of the revenue sharing blogs are doing it.
http://support.google.com/adsense/bin/answer.py?hl=en-GB&answer=1346295#Ads_on_the_same_page_or_site_as_another_publisher