Porsche also stole many of the innovative design elements of their cars from a Czech auto manufacturer called Tatra, after the Nazis took over the factory.
Hitler was not "directly behind" the development. You make it sound like he was the lead designer, accountant and test driver. He said "I want you to develop a car that will seat four, reach 110 km/h and cost a maximum of 1000 Reichsmark" because he wanted to make car manufacturing a significant industrial branch. The reality is that it was pretty much an empty promise. People invested in shares of VW so they could eventually get a Käfer, but very few were actually built during the war.