I think Mary's question was phrased properly - it asked whether you "believe" that Tarot was "originally" based on the Hebrew Alphabet. She didn't ask whether such a relationship between the two was personally meaningful to you, or whether it could have come about later.
So obviously I voted "no".
We can "know" that Tarot was not originally based on the Hebrew Alphabet as well as we can know most things in distant history - by gathering evidence and drawing conclusions. There are many kinds of evidence, and many methods for evaluating it. In early Tarot's case, all of the evidence is silent on a connection with the Hebrew alphabet, and all of the methods of evaluating the evidence make it implausible that there was a connection.
The Hebrew alphabet has 22 letters; the standard Tarot deck has 21 ordered trumps and a Fool, which are often taken together as 22 Trumps. This is the only "connection", and is at the very least a coincidence. Thus it cannot be ruled out as a logical possibility that either the inventor of this sequence of cards or an early interpreter noted the coincidence and found it meaningful in some way. But the coincidence extends no further - the names and lore of the Hebrew letters have no relationship with the images and sequence of the trumps. Thus it seems extremely unlikely that the coincidence of number has any meaning, i.e. that the coincidence IS evidence of such a relationship.
Any disinterested historian can therefore say with complete confidence, as much as can be expected in history, that the Tarot was not originally based on the Hebrew alphabet. That's the only rational conclusion.
If evidence comes up to show otherwise, it will not be shameful for the rational historian to say "I was wrong".
Ross