I have been unable to corroborate this claim, although it is known that the Nazis actively pursued the Arab leadership as allies, and did not hesitate to use promises to support Arab claims on Palestine against Jews to get their support. There is also evidence that Nazis actively encouraged anti-Semitism in Arab countries (and funded the nascent Muslim Brotherhood in Egypt) that had previously been much less antagonistic towards Jews.
Even so, it is a fascinating and somewhat plausible historical footnote to the body of literature about Nazi/Arab ties before WWII. The details in this letter, such as the Nazis promising to "return" India to Islamic rule and sharing war plans with the Arabs, are not far-fetched.
