No, they are not.
What von Daniken failed to tell his readers was the the Book of Dzyan is completely made up. It is the product of the imagination of Helena Blavatsky, the Theosophical fraud. Von Daniken merely acknowledges her as the "translator" of Dzyan. Blavatsky herself elliptically acknowledged the problem of authorship in the Secret Doctrine, where the fraudulent Dzyan stanzas appear:
"The Book of Dzyan is utterly unknown to our philologists, or at any rate was never heard of by them under its present name. This is, of course a great drawback to those who follow the methods of research prescribed by official science; but to the students of occultism, and to every genuine occultist, this will be of little moment."
In other words, Blavatsky admits the book doesn't exist except through the imaginary "astral vision" of one H. P. Blavatsky. That's good enough for Erich von Daniken!
As to von Daniken's question about the similarities among the Mahabharata, the Cabbala, the Zohar, and the Book of Dzyan: They seem to cover the same ground not because they are all reports of alien visitation but because Blavatsky used the first three as the source for the fourth, giving them a spurious connection via her fake ancient text.
In 1973 Gavin Souter asked von Daniken about the Book of Dzyan and Blavatsky's Secret Doctrine:
"It is true that in the first volume Madame Blavatsky said she had not seen the originals," said Mr. von Daniken. "In one of the later volumes, however, she said she had seen copies of the originals. No one has seen the originals, but there are copies in Hindu temples. The originals are in western China."
Of course there were but two volumes of the Secret Doctrine, but we can't very well expect someone who can't distinguish fact from fantasy to bother with details like that. (Though, for all I know, the German edition might have been divided differently.) But seriously: von Daniken's "proof" is a known fraud's assertion that she saw copies of copies of a non-existent work that had never been acknowledged or discussed anywhere outside Blavatsky's own work?
Incidentally, von Daniken's 1973 assertion that the original Book of Dzyan is "in western China" doesn't square with Gods from Outer Space, where he states that "it is not known if it still exists somewhere" (p. 137). One would think that the only text actually written by extraterrestrials would be so important that he'd have his story straight.