Is there really such a thing as stealing a common concept like Nazis and the occult? Mignola probably did take ideas from Raiders, sure, but it isn't like Spielberg and Lucas magically developed the concept of 'Occult Nazis' suddenly. They took inspiration from the older pulps and comics and serials, just like Mignola did.

Mignola's Nazis are also probably a bit more competent than the melty-faced tools from Raiders.