Arc Media

Has anyone worked with Arc Media and allowed them to operate as either a third-party adserver (to serve standard ads) or used them as a rich media vendor for building/serving/hosting rich media ads?

We have preapproved rich media vendors(Pointroll/Mediamind, Unicast...) and third-party adservers (DFA, Atlas, Mediaplex), and are pushing back on certifying an agency as an adserver. However, they are threatening to pull the campaign if we do not agree to allow them to host the ads. I'm looking for any publishers that had the same experience.