It's based on claims though ("Head of Ukraine's Jewish community claims Russian neo-Nazis fight alongside rebels"). However, it's irrelevant because you don't seem to know what a nazi is. So, two neo-nazi groups fighting each other makes perfect sense if they are from different countries. While part of the basis is the same, the other part is opposed to each other. For your information: Nazi = Nationalsozialist = _national_ socialist. While some groups put less emphasis on the extreme nationalism part, others do not.