Serbs and Croatians are white, so no, not really.
Seeing as an awful lot of Serbs and Croats in Eastern Europe died in various campaigns of ethnic cleansing in the late 20th century, it seems a bit off to use that example to claim that a particular subset of people can't be an ethnic minority just because they are white, depending on context, location etc.
Being from Eastern Europe (and, obviously, looking white) in a large, ethnically mixed, but majority white western city is still a pretty 'safe' choice for a videogame character though, but I think just putting people into the visual brackets of white and black misses an awful lot of prejudice and disadvantage that can exist for various ethnic groups that aren't always immediately apparent.