The UNHCR is responsible for the resettlement of refugees from countries to third countries: those who have entered from their home country into another country and then are seeking asylum in another country. They have chosen to simply ensure the members of Camp Ashraf renounce violence, not necessarily membership in the MeK.
It is the conduct of violence that is the key criteria for determining a person's intent, not simply the membership in an organization, and therefore we have no difficulty with the UNHCR having done that. They are the ones who do the preliminary screening and then seek countries who would be willing to resettle these individuals at that point.