Did the Old Testament prophets ever say Gentiles would receive Israel's blessings?
No. The Old Testament prophets spoke of God's dealings with Israel, foretelling Israel's Messiah and covenant promises. The context states there is not a word in the prophets that Gentiles were to receive any of Israel's blessings, because those promises were covenant ground reserved for Abraham's offspring.
Les teaches that all the prophets were dealing with God and prophesying concerning Israel and the coming of their Messiah. He says there is not a word in them that Gentiles were to receive any of the blessings of Israel. They could not, because it was covenant ground, and that was only for the offspring of Abraham. This fits Jesus' illustration: the children's bread is not to be cast to the dogs, where the children are Israel and the dogs are Gentiles. He could not take what was on Israel's table and give it to Gentiles because of the covenant promises made to Abraham, Isaac, and Jacob.