I think it is still possible that the nazis would have seized power without the soviet union.
He clearly felt slavs were inferior and Germans 'ought' to have 'living space' there
Well, first you have to explain why there is no USSR. We'll guess that the Germans decide not to send Lenin to Russia, so no October Revolution.
Can WW I still play out
mainly as OTL? Yes.
The Germans don't have to have a Brest-Litovsk treaty to treat the Eastern Front as over, shift troops west, attempt MICHAEL, and lose.
Meanwhile, Russia more or less dissolves, with anarchists, Social Democrats, monarchists, radical Socialists, reactionaries, and ethnic nationalists battling one another. It may sort out in the early 1920s, or fester like China, until some faction puts down the rest.
What does this mean for Germany? No "Red Scare"... The Bolshevik Revolution was the first success for the revolutionary left since France in 1848 - and that was half-assed. It inspired numerous attempted imitations, including the Spartacist uprising in Berlin in January 1919.
OTL - in Germany, there was a major split between the established SPD (social democratic) and the new KPD (Communist). The SPD was a major player in Weimar politics - holding office much of the time. The KPD openly disdained politics, refusing to join any government. (The crisis of 1932 was that the KPD and NSDAP had between them over half the seats in the Reichstag.)
ATL - No Sparts, no KPD. The SDP remains united and stronger. The Nazis may make a stronger appeal on the left side, getting more support from the most disaffected proletarians. However, they remain a very small forces, maybe 5%-8% of the vote until the Depression. (Even that is about double their OTL vote.)
Come the Depression, Nazi radicalism will gain them a larger block of support... but less than OTL, IMHO. They cannot pose as the defenders of order against Bolshevism. Their own radicalism and violence (which put off a lot of people OTL) is even more troubling because it has no parallel. They get less funding from wealthy people fearing Communism (none?).
The NSDAP vote would peak at under 25%, and the political establishment would never let Hitler into the government. Once unemployment started to drop, even moderately, and it was clear that the NSDAP was a political dead end, it would crumble.