This was Gushee's dissertation, and he wrote it without attention to Glen Stassen's Holistic Character Ethics method. Yet one can see the presence of Glen's method within the study, and attention to all four dimensions. Gushee is primarily working within what Stassen calls the "Way of Reasoning" dimension with a variable that will be added to his method in the new edition of Kingdom Ethics. This new variable in that dimension is what Stassen calls Historical Validation: If history is the laboratory for ethics -- an often-stated dictum with Stassen -- then the Holocaust is one of those historic moments when ethics is tested in the lab. We can learn from those groups whose morality was not sucked into the lethal Nazi ideology. That is a way of reasoning; it is attention to the traditions, methods, or convictions that helped groups and individuals pass the test of historical validation. They did not succumb to Nazi ideology because their ethical way of reasoning was strong enough to deflect it. (I think this is true, by the way, for Dietrich Bonhoeffer, as I indicated in my own dissertation. Bonhoeffer is often tauted as a participant in the assassination attempts against Hitler, but I believe that has it all wrong. Bonhoeffer didn't fail his understanding of Jesus in the Sermon on the Mount; his Christian community failed Bonhoeffer in offering him a context of peaceful resistance against the German violence machine.)
Gushee can also be interpreted as probing the Way of Seeing dimension and the threat perception variable. Nazi ideology was intent on eroding the webs of natural social connection between Jews and Gentiles (p 6). The intent was to generate active opposition to the Jews, or at least passive permission for Nazi anti-Jewish aggression. This was accomplished by advocating a strong binary distinction in which the Jews became an "out-group" and all European non-Jews were the "in-group". The "out-group" constituted a threat to the well-being of the European body politic, and eliminating that threat was important to the well-being of the "in-group". This way of seeing was a Nazi philosophical construct that persuaded Gentiles to be active perpetrators or permissive bystanders during the Holocaust (p 5).
I see Gushee working within the Passions, Loyalties and Trusts dimension with the communal loyalties variable as well when he pays attention to the out-group/in-group ideology. By creating a rift between Jewish and Gentile Europeans, Nazis placed Gentiles outside of the scope of moral responsibility, that is, outside of the scope of communal loyalties, in the formation of another kind of community devoid of any Jewish presence. Yet, the righteous Gentiles recognized Jews as belonging -- at the very least -- to common humanity (pp 167-168), and thus within the wider human community to which we owe at least basic loyalties.
This leads to what I believe is Gushee's climactic section: Chapter six. In this chapter, Gushee probes the Basic Convictions of Christians who resisted the Nazis. What he finds is that Righteous Gentile Christians held to a notion of human nature tied to the imago dei; they had convictions about compassion and love that were derived from their convictions about Christlikeness, and many of them understood Nazism to be incompatible with Christianity. To be sure, there were other influences on many Gentiles that led to their rejection of Nazism, causing them to help the Jews (chapter 5, socialization, Parent-Child relationships, experience of Discipline, Role modeling, content of their moral instruction, their experience of childhood loss, their age, gender, their politics, etc ... the Christian ethics of the Righteous Gentiles had theological as well as sociological content that influenced the altruistic behavior of Christian rescuers. Non-Christian rescuers had other factors that filled the void otherwise occupied by Nazi ideology (chapter 5), but the Christian rescuers espoused a Christian ethic loyal to traditions, and theological interpretation that was enabled to deflect persuasive lethal ideology and help their ethics pass the test of history.