The leader of the SA was gay, working class (Hated the rich and wanted a revolution, and was a veteran nationalist.
So it is entirely possible that the nationalists could've been won over from the Nazis towards a more moderate political faction.
The game allows you to have arrests and purges, which could target some nationalists and win over others. Healthcare would also win over people like the leader of the SA, as would dividing the communists and socialists. (The socialists refused to take orders from Moscow and had closer ties to Germany).
Purging the military while you are offending the upper classes, could also mean purging the upper-class interests from the military. These are all options.