Adolf Hitler was an Austrian, who used the alveolar trill [r] in his speech, not the Standard German [ʁ]. This is only to be expected for an Austrian.
According to the German Wikipedia, in Austrian German, the vowels Srandard German vowels /ə ɐ/ are replaced by / surface as [ɛ a] respectively. That means that /hɪtlər/ would be [hɪtlɛr] in Austrian German as opposed to the Standard German [hɪtlɐ], right?
However, I did listen to one Hitler speech, and he pronounced the word "aber" /aːbər/ as [aːbaː], NOT [aːbɛr]. He did however pronounce "kapitulieren" /kapɪtʊliːrən/ as [kapɪtʊliːrɛn], as opposed to the Standard German [kʰapʰɪtʰʊliːʁn̩].
So, did Hitler pronounce his own surname as [hɪtlaː] then?
Is Austrian German non-rhotic?