I've often heard that many in the west hoped that post-WWI Germany would stabilize, and eventually serve as a "bulwark against communism" in Europe. Had the Weimar Republic survived, or given way to a less insane regime, do you believe that this would have eventually come to fruition?
Weimar Germany could not serve as a military bulwark because it was disarmed.
A post-Weimar government which rearmed defensively might so function (no long-range bombers or submarines, 500,000 man army max).
It's unlikely that any non-Hitler Germany will attack the USSR (even if the Nazis are in power; Goering was opposed to BARBAROSSA, though he dared not argue with Hitler).
So that requires Soviet attack on Germany. Or a re-armed Germany coming to the defense of Poland. Such an alliance would have the support of France and Britain (and even Italy, if that matters).
As to performance - the German army would be operationally very good. Perhaps not as good as OTL, as Hitler did back Guderian and other radical innovators, overriding the more conservative Army elements. No non-dictator could do that so effectively.