Can there be 2 publishers’ ad code on the same URL?
2 publishers’ ad code on the same page
We understand many publishers would like clarification about whether displaying ads on a webpage that already contains ads associated with another Google AdSense publisher is policy compliant.
To confirm, if a website is in compliance with our program policies and the owner has given you permission to display ads on that site, then yes – you are welcome to place your ad code on the same pages as the other publisher’s ad code. But keep in mind that you may need to contact your web hosting company or the owner of the website to obtain permission to access the site’s source code.
Also, be aware that every AdSense publisher is responsible for the content of the website on which their ad code is placed.
https://support.google.com/adsense/answer/1346295?h#Ads_on_the_same_page_or_site_as_another_publisher
