DoubleClick for Publishers has a simple API to enable third-party ad networks to work with mobile publishers. This feature allows the integration of mobile ad networks that aren't already integrated with DFP.
This integration is designed to leave all ad rendering and markup decisions in the hands of the third-party network. The DFP proxy servers will return the third-party ad code unaltered to the publisher’s mobile web server or mobile device.
Here's a PDF version of the DFP Mobile Ad Network API.