It is a distinct possibility in any scenario regardless of what shade of red, white or brown Germany or Russia are. But I don't think it is inevitable. The Ribbentrop-Molotov pact and the Sino-Soviet split prove that ideology does not determine foreign policy. I could imagine a communist Germany arming more slowly than OTL being so afraid of Soviet rearmament that it prefers to co-operate with the capitalist states against Moscow.
I certainly wouldn't assume a Communist Germany and a Communist Russia would be allies - they were enemies when they were both dynastic autarchies.
After all, Marx and Engels weren't writing about Russia but Germany when they imagined the political and economic progression to a Communist state. The mantle of the "leaders of world communism" might be assumed by Moscow but Berlin would have equal claim and I suspect before long obscure philosophical differences would become didactic splits - akin to the splitting of the Catholic Church in the 11th century.
As
@Zaius points out, ideology doesn't determine foreign policy. That said, it's hard not to agree it would be hard to re-create the speed of re-armament of the Nazi era under another political regime. I also think the West would be more willing to defend Versailles (and the notions of reparations and keeping the German armed forces weak) if Berlin was under the Red Flag rather than the swastika.
It has impacts on Moscow too - whether you believe every Russian leader thinks they are Peter the Great or wants to emulate Tsar Alexander, the notion of propagating world communism on a single model is in tatters. No Internationale here, it would seem. Instead, there would be increasingly verbose and vitriolic mutual condemnation of the "pseudo-bourgeois revisionists" or the "Soviet State Imperialists" on the other.
Poland's position, between two increasingly antagonistic powers, might push it more to the West than in OTL and you would see Anglo-French diplomacy more active.
Perhaps, with more German help on the side of the Republicans, the Francoist uprising is quickly defeated and Spain moves more to the Left politically in the late 30s but aligned with Germany. Throw Italy into the mix - how does Fascist Italy deal with Communist Germany over Austria ?
World War 2? No, at least not as we had it. The Pacific conflict between the US and Japan happens as in OTL but in Europe, you'd have a more complex set of relationships and "alliances". Does the USSR still contemplate expansionism? I suspect not.
It's possible German "Communism" will evolve by the 30s and 40s into something very different from Soviet Communism - more workers' control of factories, no collectivisation - perhaps what Gorbachev called "perestroika" would be "Offentlichkeit" or something similar - the State supreme but more willing to hear other voices. Economic growth doesn't mean the middle class disappears and prosperity is often the driver for reform. Could we see something more like our social democracy by the 50s and Brandt still as Chancellor but pursuing detente with the rest of Europe in the 60s and 70s?
