This is not a new phenomenon. We learn from Melachim Bet chapter 17 the King of Assyria brought foreigners and settled them in the Shomron. These people were idolators and Hashem sent lions to attack them. When this happened the people told the King that they didn't know the law of the G-d of the land so he sent a Kohen to teach them. It is interesting to note that the Kohen settled in Bet-El. According to the commentary the Kohen realized he couldn't convince the people to give up their idols so he allowed them to continue serving their idols but as intermediaries not deities. They feared Hashem but they continued to worship their own g-ds in addition to Hashem. We see these foreigners later in Ezra chapter 4 when we come back to the land from Bavel to rebuild the Beit HaMikdash.
The enemies of Judah and Benjamin heard that the people of the exile were building a Sanctuary for Hashem, God of Israel. They approached Zerubbal and the heads of families and said to them, "Let us build with you, for, like you, we will seek your God; it is to Him that we have been sacrificing since the days of Esar-haddon, king of Assyria, who brought us up here." But Zerubbabel, along with Jeshua and the rest of the family heads of Israel, said to them, "It is not for you together with us to build a Temple for our God; rather we by ourselves will build it, for Hashem, God of Israel, as King Cyrus king of Persia has commanded us."
According to the commentary, these people had adopted a distorted form of the Jewish religion worshiping Hashem along with their gods.
Sound familiar? Is not the slogan of the so-called "xian zionists", "we worship the God of Avraham, Yitzhak, and Yaakov just like you"?