thanks about the reply but let me try to rephrase my question and elaborate a bit further.
I have a client X whom using DFP as a delivery-system / ad-server. He manage on DFP a lot of line items (with special targeting as geo, browsers etc.) and creatives.
I want to fetch those line items/creative from his DFP account to my own self-developed platform and serve the ad to the user.
This means X will manage his creatives on DFP while my platform will serve the creative to the end-user using all the targeting/restrictions the creative has on DFP; but I would like to keep DFP reports in the loop and count impressions/clicks etc. there as well.
To do so I thought about to ways (which I'm not completely sure it can be done, I've just started to read DFP API documentations):
A. I will fetch all the line items/creatives every 10min to my platform but I still need somehow to notify DFP about successful impression / click that my platform counted.
B. Using programmatic integration similar to OpenRTB to get creative in response to a request my platform will send to DFP (with all the user details etc), but I will need to get the raw creative from the line-item and not a tag.
Thanks