Q: How is it that we find so many Greek names of great men in the Talmud? And we know, "Shelo shinu es sh'mam," not to change a name is an ideal?
A: The answer is this: Nobody ever gave a gentile name to his child. But we have to realize in ancient times there was a tremendous number of converts, geirei tzedek, of very high quality. And in the olden days, it was not a custom to change the names. Today we change the gentile name. We call him Avraham or something else.
They came in with their names and they kept their names. Munbaz remained Munbaz, although Munbaz became a tanna and in one place we find him arguing with Rabbi Akiva, he was so great. But he was still Munbaz. They kept their names. Now, when these great tzaddikim were geirei tzedek. They were men who illuminated the Jewish world with their wisdom.
Onkelos HaGer — Onkelos is a gentile name. They didn't change his name. Onkelos! He's in the Chumash. He's higher than Rashi! Rashi brings him as a proof. He's on top of Rashi, right next to the Chumash! They didn't change the name. So when in some future generation, someone wanted to honor that ger, or someone wanted to give his child that zechus, he called him that name. That's how you got the names. It was from geirim, they were named after geirim.
But nobody in the ancient times named his child after a gentile or gave a gentile name. It's a good question, but the answer I think is in place. — Shir Hashirim 5 (#75)
 Vayikra Rabba 32:5
 Shabbos 68