I've read this circulated over the years as fact, and attributed to different things – most commonly that the Nazis compared the Jews to 'dirty rats', and saw Mickey Mouse as holding the mouse up as an ideal.
That seems far-fetched to me, but I'm wondering if there is any truth to the idea that Hitler or other high-ranking Nazis hated Mickey Mouse (or had any feelings about the character at all).
The second volume of Art Spiegelman's wonderful graphic novel Maus starts off with a famous quote from a Pomeranian Nazi newspaper calling for the downfall of Mickey Mouse, which has popularized a notion that the regime despised Disney.The Third Reich's stance on Disney and its products is somewhat more complex. Certainly a number of cultural luminaries within Germany decried Disney and it had three strikes against it: Disney animation was not German, it was in a medium that embraced a mass cultural society with its attendant capitalist merchandising, and Disney cartoons were popular among the German public. All three of these factors were invoked against Disney among various cultural critics within the Third Reich. The rationale for much of this criticism predated the Third Reich, for example, there were campaigns against Schund (trash- i.e. mass market) literature in the 1920s and such criticism would continue after 1945. One prominent example of the latter was Thodor Adorno (certainly no Nazi!) attacked Donald Duck as an example of how mass society engenders apathy among the proletariat.
However, much of the state campaign against Disney stemmed from the Third Reich's cultural policies to stimulate native German arts which amounted to tariff on the non-German media. The Third Reich quadrupled import duties on foreign films or tried to arrange a quid-quo-pro trade deals by which foreign film companies would have to accept German films if they wanted to show their products in German cinemas. These policies drove out many American companies and Disney found that they could seldom turn a profit in Germany despite their products' popularity.
Despite the low and mid-level attacks upon Disney, some higher ranking Nazis were fond of Disney's animation. Goebbels famously considered Snow White a masterpiece. On the occasion of Hitler's birthday in 1937, Goebbels gave his master eighteen Mickey Mouse films and his diary noted that Hitler "is pleased to no end." Like Goebbels, Hitler also had a special print of Snow White and apparently screened it.
Sources
Evans, Richard J. The Third Reich in Power, 1933-1939. New York: Penguin Press, 2005.
Giesen, Rolf, and J. P. Storm. Animation Under the Swastika A History of Trickfilm in Nazi Germany, 1933-1945. Jefferson: McFarland & Co., Publishers, 2012.