The main core of the Ganz story is that it's claimed that Hitler and Porsche saw Ganz's 'Standard Superior' at the 1933 Berlin motor show and was subsiquently arrested by the Gestapo and his design stolen by Porsche.
What is a little unclear is exactly what was 'stolen', because the Volkswagen didn't look like the Standard Superior so it clearly isn't the exterior design. Is it the format of the car, backbone chassis and rear engine format? The problem with that is that these aren't things that Ganz invented. So is it the concept of a small affordable car? Because many companies had expressed a desire for this since the Model T. The documentary also makes it sound like Ganz invented aerodynamics!
The other issue with the Ganz version of events is that it completely dismisses any of the work that Porsche had done up until 1933 and assumes Porsche had nothing to work with at the start of the peoples car project.
Lets be clear, Ganz was an extremly influential figure in the German motor industry due to his position at the Motor-Kritik magazine. There's no doubt that his critisism of the old fashioned designs being released by the established car manufacturers at the time had a lot of weight and Hitler did not wan't him in the position he was. What Ganz was good at, was pushing the car industry forward by promoting the ideas of 'modern design'. His influence on the industry is what Ganz should be remembered and celebrated for.
The design of the Beetle was credited to Ferdinand Porsche, because Porsche was head of the people's car project design team at that time, but in truth there were a handful of designers who were pushing design ideas at that time. Each building on others ideas and evolving them further, finding the person who did it 'first' is almost impossible.
It could be argued that the true father of the Beetle was Paul Jaray. Jaray started out desiging Zeppelin's, from this Jaray understood how air flowed around moving objects and started applying his ideas to cars. Jaray was working on designs that could be considered 'Beetle Shaped' way back in 1922:
This design differs from the Beetle in that the engine is in the front. The rear engine concept came when Jaray was working with Hans Ledwinka at Tatra. Ledwinka is also credited with inventing the backbone chassis, leading the Tatra to be a very similar design concept to the Volkwagen. Asked if Porsche had copied from Ledwinka, Porsche replied 'Sometimes I looked over his shoulder, sometimes he looked over mine'.
Porsche himself was interested in the small affordable 'peoples car' concept and designed a small car for the Zundapp motorcycle company. The Type 12 featured a rear mounted five-cylinder radial engine at Zündapp's insistence, rather than the flat four Porsche preferred. Porsche designed the Type 12 in 1931 with prototypes being built in 1932 - designed 2 years before the Berlin Motorshow Ganz claimed Porsche 'stole' his design.
Around the same time as Ganz was working on his 'Volkswagen', Tatra were working on their own small car. Here is the Tatra V570, designed by Hans Ledwinka's son Erich Ledwinka using Paul Jaray's streamlining patents. This car was released in 1933, the same year as Ganz's Standard Superior. The Tatra featured a rear mounted boxer motor and a backbone chassis.
What this demonstrates is that a number of designers were working on the small car concept, all trying to use 'modern' design techniques and construction. The format of a backbone chassis and rear engine car, with an aerodynamic body was a popular idea in 30's Europe. There are numerous other attempts by other manufacturers with this concept, from Mercedes, NSU, Skoda and even Rover.
Porsche's version was the Volkswagen and it succeeded due to state backing from Hitler who built a huge factory for it, which was utilised and revived by the British Army after the 2nd world war.
So in my opinion, Ganz played his part, he is a forgotten figure in this period which is a huge shame, he should be rememberd and celebrated - but he did not design the Volkswagen and Porsche did not steal his design. Incidentally, the body design of the Volkswagen Beetle wasn't actually designed by Porsche - it was designed by Porsche team member Erwin Komenda.