I'm not sure if the Doubleclick AdExchange allows that but sometimes it can look like it's coming from Adsense or Doubleclick AdExchange but the ad is actually

I'm not sure if the Doubleclick AdExchange allows that but sometimes it can look like it's coming from Adsense or Doubleclick AdExchange but the ad is actually served from Doubleclick For Publishers. In that latter case the publisher decides what is acceptable.