"certain light-skinned people – currently called “white,” though a multisyllabic name like “Cvjetanovic” might not always have made the cut..."

Actually, Denise is aware that racism is not necessarily based on color, and she's made this point many times.  In NA, we tend to think of racism as based on color like black versus white in the US.  But the sort of racism the white nationalist/Nazi movement supports is the sort of racism Hitler practiced, where race also means a cultural group, and just being white isn't enough to be part of the "race."  

The observation she's making in this case is that in Hitler's Germany, it was illegal for Germans to marry white people with last names like Mr. Cvjetanovic's because they were not part of Hitler's Aryan race.

Nobody said white racists can't be racist against other whites.  Britain's mistreatment of the Irish certainly would fall into that category.  And there are also examples of racism among black and Asian groups.