I'd love to believe it, but:
Three years before Hitler described 'his idea' to Mr Porsche in a Berlin ...hotel, Mr Ganz was driving a car he had designed called the Maikaefer, or May Bug.
The lightweight, low-riding vehicle looked very like the Beetle that was later developed by Mr Porsche, who is still considered the foremost car designer in German history.
Jewish inventor Mr Ganz had been exploring the idea for an affordable car since 1928 and made many drawings of a Beetle-like vehicle. - Your Jewish News
Image from the book's Dutch site.
The evidence doesn't add up.
This car is smaller than a Volkswagen and shows none of the design innovations.
Hitler saw the May Bug at a car show in 1933 and made sketches.
'Ferdinand Porsche drove Ganz's prototype in 1931. I found a lot of evidence that all similar rear engines in the 1930s can be traced by to Ganz.
Further, Porsche (the designer, not the company, which incorporated in 1931) had been making rear-engine small cars for some time.
In 1898, [Ferdinand] Porsche joined the Vienna-based factory Jakob Lohner & Co, that produced coaches for Emperor Franz Joseph I of Austria, as well as for the kings of England, Sweden, and Romania.
Their first design, unveiled in 1898, was the "System Lohner-Porsche", a carriage-like car driven by two electric motors, directly fitted within the front wheel hubs, and powered by batteries. This drive train construction was easily expanded to four-wheel drive, by simply mounting two more electric motors to the rear wheels as well, and indeed such a specimen was ordered by the Englishman E. W. Hart in 1900.
Though over 300 Lohner-Porsche chassis were sold up to 1906, most of them were two-wheel drive—either front- or rear-wheel driven trucks, buses and fire-engines. - The People's Encyclopedia-Blog: "Ferdinand Porsche"
Further, his career had been tending toward smaller and lighter cars:
Porsche's concept of a small, light-weight Mercedes-Benz car was not popular with Daimler-Benz's board, however.
Even more damning for Ganz, Porsche had been building Volkswagen-like cars, which is why Hitler handed him the contract.
From 1931 Ferdinand Porsche and Zündapp developed the prototype Auto für Jedermann ("car for everyone"), which was the first time the name "Volkswagen" was used. Porsche preferred the 4-cylinder flat engine, but Zündapp used a water-cooled 5-cylinder radial engine. - The People's Encyclopedia-Blog: "Zundapp"
This was an expansion on his proposed design for Mercedes. It was built in 1931, so unless we believe he cooked the thing up overnight after seeing the Ganz car, after having built rear-wheel drive cars for two decades himself, we see that Ganz was entirely irrelevant to the Volkswagen.
The Zündapp prototype follows up on all of Porsche's work until that point including the Mercedes prototypes.
I would like to believe Ganz, but the record does not stand up in support of his allegations.