First we have to find out what accent Hitler did have.

He was born into a family which would have been described as "gutbürgerlich"(approx. upper middle class) hadn't he been so keen on keeping his heritage a secret. His birth took place in 1889, in Braunau, a small city in what today is Oberösterreich, next to the Bavarian border. He learned to talk in Passau(a city in Bavaria, close to where the Czech, German and Austrian border meet) where his family lived between 1892-94. He went to school in the very rural Lambach from 1894-98. During his teen years he lived in Linz, which back then was a thriving metropolitan area of the turn of the century Austria(not so much today). He wasn't a particularly good student, but he showed remarkable social ambition, and as such tried to get rid of his accent and speak proper High German(But we don't know what his accent sounded like at this time).

Later he lived in Vienna and Munich, but it seems like he didn't pick up either of the very distinct accents of the cities.

The recordings we have of his voice are almost exclusively of post 1932 speeches and are as such pretty worthless as to find out what he would have sounded like in the beginning of his political career. First of all his speeches were highly orchestrated masterpieces, not in their message of course, but the way he built up his speeches was nothing short of mesmerizing. Most times we only see short clips of his exstatic shouting, but those were only the climaxes of his speeches, preceeded by a long, well thought out build-up. Uncommented raw material is still hard to come by, exactly because it is still dangerous today.

What's more is that he received formal voice training by an opera singer in the early thirties, further influencing his speech patterns.

All of this resulted in a rather uncommon accent. Most notable is the "rolling R" which gives away that he's either Bavarian or Austrian, everything beyond that is harder to tell. You can tell that he was not Frankonian or Tyrolian. He sure wasn't from Vienna or anywhere in the Pannonian bassin.

So yes, he did have an accent, but not a distinct Austrian one.

Unfortunately I can't answer your question what his temporaries thought about his accent, since I haven't found any commentaries about this ever.

I can't give you information on Hitler in particular, yet on people from this region in general. People in (most of) Austria and Bavaria speak the same dialect (group), Bavarian. Also his place of birth, Braunau sits pretty much on the border between Germany and Austria. Thus someone from there should be indistinguishable from people in south-western Bavaria by dialect/accent while speaking Standard German.

When he was anywhere in the region of Bavaria/Austria/Czech Republic, he would have pretty much sounded normal. The Bavarian dialect is very thick and unmistakable to most Germans.

When you listen to a good recording of his voice however, you can hear that his accent isn't all that thick. You don't really have to listen very hard to understand him. This is not always the case. I have spoken with or heard some people from the Bavaria/Austria area, that I really had to pay attention to every word.

Getting back to his accent though. It sounds like he trained himself to speak more "High German". High German is the "official" variant of German and what you are taught in school and hear on the news, read in publications, etc. It is the most clearly understood form of German because it is mostly "accent-less".

Source: Am German and hear it every day.

He had the distinct southern R when he first came to power and he didn't drop it till the very end. The other Weimar era politicians, from the reactionaries to the communists, usually spoke proper Hochdeutsch.