I am stating that those individuals of Serbian ancestry, I would accept as fellow Serbs, regardless of religion, if they as well see themselves as such, if not then not. Others I would accept as citizens of the nation.
You can chose how to identify, with which nation, but you cannot chose what you are, that is given by birth, for you to embrace it, or not.
P.S. It is not false to identify with a different nation than your ancestry is, if you were born there, living there, not discriminated against, feeling accepted and comfortable there. However denying your ancestry is always frown upon as lack of dignity.
Nationality is rather subjective category. Miloradovići were of Serbian ancestry, they were very proud of that but again, they lived in Russia, they participated in Russian culture and politics and they identified themselves as such. They were Russian. Simple.
As far as some Euroepan (in broader senes ie white) chose to identify himself or herself with Serbs he is Serb, taht is how things looked like for major part of our history. Yes, Serbs mostly originated from Slavic wariors invited by Roman (Byzantine Empire), but there are Illyrians (who left lot of their genofond, Greeks, smaller slavic tribes Timočani for example…)