Noo one cares about alliances and such stuff. After all, it is a nations cup, not a "we have the same cultures so we can play together"- cup... Russia and Ukraine are actually two (geopolitical) separated countries, so no, don´t let Ukrainian people play for Russia. I don´t see why you are even discussing this, after pages over pages concerning the scotland/gb "issue". If you have relatives and stuff and it is going along with the rules, mix the people.. But in general don´t mix up countries in a nations cup.
Okey, but why Czechs and Slovaks play like one team? Why Norwegians and ppl from Denmark play like one team? And third question, why Russians can not play with Ukrainians in one team?
But thank you for it at least
Spoiler
If you have relatives and stuff and it is going along with the rules, mix the people.