Yes, Hitler was a socialist. Before his rise to power, he vigorously defended himself against charges by Goebbels and the Strassers that he was a petty-bourgeois and not a true socialist.
Gregor Strasser could be counted as some sort of a "nationalist socialist" (
http://en.wikipedia.org/wiki/National_Bolshevism). Of course, he was executed after Hitler took power.
When it comes to "National Socialism", a certain nuance is also lost in translation. There's a difference between
Nationaler Sozialismus and
Nationalsozialismus. The Nazis always emphasized that they adhered to the latter (and opposed the former). In English both terms are translated into "National Socialism". I guess that's also the reason why you can find so many "Hitler-was-a-socialist!" threads in English-speaking forums.