Well he did have a Bavarian accent. Germans, especially from the Bavarian regions do their best to speak standard-German though it has some hardships. Especially the "R", which is spoken way softer in the standard-German is way harsher in Bavarian dialects. This can be easily heard in Hitlers speeches and gives them what some call "aggressiveness".

Also Hitler came from the "Innviertel". This region belonged to Bavara until the late 1700s and the people there until today don't fully speak the typical dialect one would call "Austrian", although Austria does not have a dialect shared by all of its regions.

Hitler spoke therefore standard-German though one can clearly hear he speaks naturally a Bavarian accent. Especially the Germans from the north can't really understand Bavarians when they speak in their various dialects very well. He therefore as politician was forced to speak standard-German.

First, to explain a bit the difference between Austrian or Southern German accents: Technically Austrian belongs to the Bavarian dialect (Südbairisch). You will hardly recognize austrian from bavarian, but there are several much stronger rural austrian accents, like carinthian, tyrolean, styrian, viennese (not rural, but different) which deviate from the main austrian dialect, but are still titled "Südbairisch". So, it's the same.

Where he came from, the Innviertel is at the border of Bavaria and Austria.

Every Austrian and most Bavarian politicians, actor and news reporters speak the official german "Hochdeutsch" from the "Benrather Linie" (Frankfurt). This is how you learn it in school, and esp. as politician or public figure you want to target more people. He spoke publicly in "Buehnendeutsch" with a very strong rolling "R" on purpose, to raise the dramatic effect.

Hitler did have an Austrian accent, but it wasn't a very strong one. And no, he did not have a Bavarian accent, as he did not grow up in Bavaria.

Hitler was born on a city which still borders Austria and Germany. But at a very young age, his family moved to Linz. It was in Linz that Hitler grew up and he left Linz just after he left school (he left school since they offered him that choice, otherwise they would have thrown him out). From Linz, he lived literally as a tramp in Vienna (he stayed at an infamous 'men's hostel' near the Ostbahnhof in Vienna).

After his stay in Vienna (at about the age of 23), he left for Munich. Since Hitler had no work ethic to speak of, he painted postcards and sold them to the tourists in Munich in order to survive. He did this until August 1914, when the war broke out. He was 25 at the time.

From roughly the age of 23 to his death in 1945, Hitler lived in Germany (the only exception was in Belgium/France during the First World War, with his Bavarian Regiment).

One can clearly hear that Hitler never had a 'Bavarian' accent, as his accent lacked the intonation of any Bavarian accent. If you want to put a label on his accent, you would have to say an 'Upper Austrian' accent, as that is what the Linz area is called.

A very good recommendation to read about his life is Joachim Fest's book.