Is it possible for a university to participate in a DN, to collaborate and provide mentorship, and not have to go through the accreditation agency?

Formally if there is not an accreditation, then it would not be counted as a joint, double or multiple degrees.The policy objective behind the DNs is mutual recognition and capacity building and to have the same recognition of the doctoral degrees from the different universities and different countries at the same level. It is difficult but just providing mentorship would not qualify completely.