I had to deal with Morey's contention in some depth to uncover his deceptions and mistakes because his speeches and writings have misled many people. But at the end of the day his theory is rather silly.
Even if he was able to show that the North Arabs in Mecca worshipped the Moon-god, and even if he was able to show that they used to call this Moon-god Allah, this still does not prove that Allah in Islam is a Moon- god. To prove or disprove this he needs to show what the Qur'an teaches about moon worship. The Qur'an, however, clearly refutes moon-worship. The Qur'an says: Adore not the sun and the moon, but adore Allah who created them ... (Qur'an 41:37).
But Morey is not interested in letting his readers know what the Qur'an says. In his book The Islamic Invasion Morey gave a description of the Sabaeans and their religion. He says: The Sabeans had an astral religion in which they worshipped heavenly bodies. The moon was viewed as a male deity and the sun as a female deity. Together they produced other deities such as the stars. The Qur'an refers to this in Sura 41:37 and elsewhere (Morey, Islamic Invasion, p. 42)
Morey mentioned Sura 41:37 from the Qur'an but he did not reveal what the verse says. But I have quoted it above to reveal what Morey wishes to conceal. If he would let his readers know what that verse says his deception would crumble. He did not even say that the Qur'an in that verse prohibits the worship of the sun and moon. He merely says that "the Qur'an refers to this in Sura 41:37 and elsewhere." If his readers understand from this that the Qur'an accepts the worship of the sun and the moon, Morey's aims would be accomplished. Morey should realize that as a scholar he has an academic obligation to make honest use of his sources. He should also recall that as a Christian he ought to speak the truth always.