Google has made change to its policy of AdSense and according to new policy, you can run Google AdSense on same page with Yahoo advertisements. It is one of the most significant changes in AdSense during recent times.
It was noted about the removal of a particular phrase in policy which went like –
We do not permit Google ads or search boxes accessing Google search services to be published on web pages that also contain what could be considered competing ads or services. If you have elected to receive contextually-targeted Google ads, this would include all other contextually-targeted ads or links on the same page as Google ads.
So one part is clear but other one, which is Yahoo/YPN, still has problem with the competitor advertisements on same page as the YPN policy goes like –
For any webpage or RSS feed that includes the Ad Code, you agree not to display or link to any other advertising (including but not limited to any listing) that is mapped to or responds to the content of the Ad Page
Therefore, as far as AdSense is concerned, you can have other advertisements on the same page (as far as the color schemes are different). Hopefully, Yahoo will also be considering its terms and conditions as it wouldn’t like to loose competition that easily :).