Though I completely understand why you would dismiss Hitler's or Spengler's versions of 'Socialism', I feel that Socialism had some changes and differed between many factions before experimenting with it into practice. Mensheviks, Bolsheviks; Rosa Luxemburg disagreed with Lenin on some points as did Trotsky and Stalin, all of these did not exactly follow Marx's doctrine tit for tat. So if Hitler felt that his version of Socialism worked for his country I won't go to say he is not a "true" Socialist (but not a Marxist), after all prior to the start of WW2 he did accomplish quite a bit for Germany. Spengler to be fair to his point, socialism is a German idea.
We don't say there is only one right path to capitalism do we? Policies differ from countries like the US and Norway for example. It has also changed from what it was when capitalism first began, so I don't see why we stubbornly hold on to the idea that socialism can only be Marxist socialism. If we are to talk about founding fathers of a Socialist society aren't we overlooking the Spartans?
Marx invented the term "utopian socialists" to differentiate his theories from the others – coming up with that derogatory label for them. (He claimed his version was scientific, unlike theirs.) We don't call either Marx, St Simon, Fourrier or any of the rest "capitalists". We don't call them "liberals" either, despite Marx claiming that all he knew about "class struggle" he learned from the liberal historians the brothers Thierry. The "reform socialists", the Social Democrats, also did not follow Marx, and for that ended up labeled "social Fascits" by the Soviet-led Comintern, with the directive the "real" enemy wasn't the Fascists or Nazis, but the Social Democrats.
The connecting bit between the USSR and Nazi Germany, or Fascist Italy, was always the totalitarian dictature aspect, ahead of any other ideological considerations. It's something derived from fetishizing the all-importance of The State, which made both at least theoretically very keen on autarky, economic included. But then the Soviet ideology was universalist in character (shared feature with Liberalism and Conservatism), while the Nazi and Fascist ideologies were parochially nationalist in character, with the Nazis upping the ante with blatant racism.
And it's still a salient feature that as racist, nationalist and autarchic the Nazis and Fascists went, they never abolished private property (subject to their ideological considerations of race of course) of expropriated the assets of their capitalists, rather co-opting them under the umbrella of the expanding powers of the race-based increasingly autarchic state – which otoh was supposed to grow through military conquest, which in turn was set up so as to let the politically loyal, racially acceptable German capitalists to grown their businesses at the expense of defeated nations and races. That certainly wasn't how the Soviets did it, or how Marx envisioned anything.
