*Pseudo-Intellectual Who's Heard A New Word But Doesn't Know What It Means Alert*
First of all, the proper word for the faith is "Zarathustra". "Zoroaster" is a Greek corruption. Secondly, Zarathustrianism is a dualistic theology. Tolkien's theological myth structure is monotheistic - very Catholic, in fact.
Not that I have any good reason to defend these misguided pagans, but having met a few "(east) Indian-American" Zoroastrians recently, I read this about them:
"Zoroastrianism is the ancient religion of Persia. It was founded about 3500 years ago by the prophet Zarathushtra. Arising out of the polytheistic traditions of ancient India and Iran, he was one of the first monotheists in human history. Zarathushtra preached that there was one God, whom he called Ahura Mazda. Ahura means 'Lord,' and Mazda means 'Wise,' so Zoroastrians call God the 'Wise Lord.' "
Of course, Tolkien's Catholic theological myth structure is "True Myth".