I would like to share the response from Google in question to add more advertisements on the same page of another network. AdSense publishers may display ads from other contextual ad networks on the same page as Google ads only if the formatting or color scheme of these ads is sufficiently different from the layout of the Google ads. In other words, if you choose to place non-Google ads on the same site or page as Google ads, it should always be clear to the user that the ads are served by different advertising networks and that the non-Google ads have no association with Google. If the formats are naturally similar, we'd ask that you use different color schemes for the competing ads. So the conclusion is that if the ads are different and you don't try to copy the way google ads look is ok. If a message Ads by XX network is displayed is ok also as it makes it different.
I didn't find any clear answer like this (I get tons of results) so you can use whatever ads but not make them look like google at least change colors. This is good I was really afraid to break TOS. One last thing I would like to find out is if you can use a banner rotation script that can display adsense as default and rotate with other paid banners.