Well I know next to naught about SCRA, apart that they are communists in a galaxy that hates them right now minus the minority. They need all the help they can get (but won't admit it), so allies are very valuable.
Should the Red Hessians go to war with whoever, maybe Rheinland, I can see SCRA jumping in to 'fulfill' the extermination of their ancient political enemies by carrying out their orders. Not to mention they could make great resource and monetary gain if they manage to blast their way into the capital and interdict the trade convoys. Piracy, yes, but every army needs fuel and money.
I can see it to be logical that SCRA joins the Red Hessians in war to honor their pact, and gain some ground in Sirius.