Actually, if the Soviets DOW the Germans, they get several disadvantages:
1) CG demand is fixed at around 50% (compared to 10% if Germans DOW them instead)
2) They get the usual 10% dissent hit (maybe no biggie, but still a bad thing)
Also, if the Soviets DOW in 1939 (during the phase when Germany usually takes France), the also get:
3) Piss-poor tech
This exact thing actually happened in the just finished DEG8. Soviets DOWed Germany (me) in late 1939, rolling through the basically undefended parts of Poland and eastern Germany with 100+ divs. I strat redeploy around 15 mech-A, and totally kick their butts (31 divisions captured, about 12 of which were armored). After stabilizing both fronts, it takes me and Italy about 6 more months to finish off the French (human played), after that it was just a cake walk.
As long as the Germans either finish off France quickly (I admit I did not exactly do this in the above mentioned game...) or keep some sort of sizeable force in the east (which I actually did not do either....) then a Soviet DOW should not be a problem for the Germans.