One of the organizers was UNDP, a secular organization. The topic of seminar war "Engaging with Religious and Traditional Peacemakers", and the practical purpose of the seminar was to start building a network of religious and traditional peacemakers to assist UN peace mediation, to bring their cultural insider knowledge to aid third party conflict resolution.
http://www.kirkonulkomaanapu.fi/en/about_fca/advocacy_work/finn_church_aid_appointed_to_develop_religious_leaders_peace_mediation_network/?id=2720
http://blogs.timesofisrael.com/religious-leaders-as-peacemakers/
I can't find a full list of participants, but seems there were also secular activists and NGO's and their representatives attending, and the organizations mentioned such as Finn Church Aid has many partnerships also with secular organizations.
So at least in this case it does not sound like there is cause for worry of exclusion of non-believers, as this is a UN project to gather network of cultural (religious and traditional) knowledge to help peace mediation.