Ezriel Guenzig (1868-1931) was a Orthodox rabbi in Moravia and later, he became the head of the Mizrahi Tahkemoni School in Antwerp. In his time, as editor of the journal Ha-Eshkol, he was a conduit of Western and academic knowledge to his Hebrew reading rabbinic audience; unfortunately, he is remembered little today. Besides Hinduism, Guenzig wrote on Abulafia and other interesting topics. It seems he was influenced and even wrote a book about Fabius Mieses, the source for Rav Kook’s knowledge of modern philosophy. And his journal Ha-Eshkol is available as a free android app.
In 1900, he wrote an appreciation of the recently published works belonging to the series Sacred Books of the East edited under the direction of Max Muller. He compares the Hindu positively to Judaism, noting the similarities of the two religious worldviews Kabbalah and Hinduism, especially emanation, nirvana, eyn sof, sefirot, and theories of the soul. Guenzig’s approach consists of focusing on the Vendata philosophic works and the ancient Hindu scripture to formulate a Hindu monotheism, which he then connects to his own Perennialism. Mentions of Indian thought in Rabbinic thought in the first part of the 20th century proceed in a similar manner. Note his labeling monotheism as the “moral foundation” for humanity gained through cultural evolution.
In perusing these works we find many concepts and images, mores and customs, principles and many doctrines that also stand in the highs of our religion. We see astounding similarities in many ways between the faith of the Hindus and the faith of Israel, not just in details but even in the principles of purpose, their studies, and their opinions…Just as the Therapeutae in Egypt brought Neo-Platonism into Judaism, the Essenes in Judea brought the secrets of Buddhism- the masters of secrets in India- to the masters of secrets in Alexandria and other Jewish works who, in turn, brought these allusions in the secret of our holy writings.
The belief in the Oneness of the creator and the unity of existence is a sublime step in the cultural evolution of humanity, the moral foundation for all religions of Enlightened peoples.
Also the [Hindu] doctrine of the relationship of the individual soul to the universal soul and the spiritual perfection by cleaving to divinity, freed from all desire and physical lusts… is found in many Jewish believers and also is found by our ancient wise and the early kabbalists who followed them.
If a scholar delves into the Vedas will see that the early kabbalists, the fathers of the philosophic Kabbalah most of them followed the Hindus…
Ezriel Gruenzig, “Hindu Philosophy and Kabbalah” [Hebrew] Ha-Eshkol 3 (Cracow: 1900) 40-48.
The Book of Doctrines and Opinions: 
Not wholly relevant to the post, but do you recall the term you once used to refer to the idea that the ancient Greeks, e.g., believed in one god above all the other gods?
henotheism.