What I mean is, is it plausible for another charismatic firebrand agitator in the same vein as Hitler ...to achieve some kind of political power in West Germany?
Not unless there is a disaster comparable to the Great Depression. One must remember that Hitler and the NSDAP was active for many years with minimal political success. In the election of 1928, the NSDAP got less than 3% of the popular vote. It was only after the economy crashed that its vote grew to significant levels.
Something comparable would have to happen in post-war Germany - not necessarily an economic crash, but something that would cause a large proportion of the people to turn against conventional politics.