...
AdEngine supports additional ad units in the page, externally created through the googletag object in GPT. These can be Ad Manager only units, a special campaign, etc., that are not directly set in AdEngine, but can be managed by AdEngine on in pair with the other units.
To add these units to AdEngine, the adngin.cmd.setGoogletagAdSlotElementIds() api API function needs to be called as a part of AdEngine's functional configuration. Alternatively, it can be added using declarative configuration.
...
Adding GPT ad-units to AdEngine will pass them to the Google Ad Server additionally to the AdEngine ad-units during the auction process. This improves page performance by using a single request to refresh all ads. It will also simplify the page code as there no extra code required to to manually call the ad server for the additional GPT ads.
...