The book of Hebrews was NOT written to Hellenized ‘Jews.’
It was written to the same people to which Yeshua was sent: The Lost Sheep of the House of Israel.
Hellenistic Christian Jews would certainly be considered the lost sheep of the house of Israel. Hellenistic Jews simply means diaspora Jews. The author of Hebrews quoted to his readers the Greek Old Testament, not from the Hebrew, and so that is why the book must have been written to Hellenistic Christian Jews.