I think linguistically, the most probable answer is that ancient Hebrew had a 23rd letter. Jeff Benner does a phenomenal job explaining this theory and even made a youtube presentation. I found an interesting article in The Curse of Ham - Race and Slavery in Early Judaism, Christianity, and Islam by David M. Goldenberg, pp. 146-47.
Whether or not it is related, at least one Rabbi has said that there is a letter missing in the Hebrew alphabet. See Sefer ha-Temunah, 62a; David ibn Zimra’s Magen David (Amsterdam, 1713), 47b. According to Lawrence Kushner, author of The Book of Letters: A Mystical Alef-Bait, Sefer HaTemunah teaches that "every defect in our present universe is mysteriously connected with this unimaginable consonant", and that as soon as the missing letter is given to us, our Universe will be filled with undreamed of new words, the words that will turn repression into loving. He says it is the shin, but I believe that ghayin is more logical.
So it is quite possible that this root was originally bifurcated as well: one meaning to enter and another meaning to mix. Balashon appears to allude to such, but never makes the connection, as does Mitchell First and Dr. Rabbi David J. Zucker. Menashe Har-El (citing Yechezkel Kutscher) is the only source I can find at the moment who writes that the the root arav is equal to the Arabic root gharb. Even the Zohar takes advantage of this multivariate linguistics. See From Metaphysics to Midrash - Myth, History, and the Interpretation of Scripture in Lurianic Kabbala by Shaul Magid, pp. 84 ff. In light of the following, then, there is no connection between the erev rav and Arabs.
This would explain why I cannot find any connection made by the Rabbi's (at least in my library). The Gra writes in Kol HaTor, Chapter 2:2, that the Erev Rav are heads of the Jews in exile. Rabbi Pinchas Winston writes about them on parshas Toldos and Behaaloscha. I also found this lengthy pdf that collects many sources. If anything, the Erev Rav mixes Edom/Esav and Yishmael (who are traditionally ascribed as the progenitors of the Arabs).