About using former German divisions, how many men could they seriously muster for this? I can't imagine more than a million at the most. Both Britain and he US had about 1.4 million German prisoners in total spread across North America mostly (I'm imagining not all of them would be combat worthy or willing). German units IN Germany itself well shit you'd be lucky to get together 50,000 combat worthy German soldiers, most of the men are dead, wounded or MIA and made up of Teenagers and Grandfathers. I don't think they make much of a difference and 4 years of anti-Nazi propaganda isn't just going to go away like that, Allied troops are going to greatly resent German soldiers after the death camps were broken open so there is going to be issues there.
Another thing is people put a lot of faith into the Atomic bomb, if I recall correctly, the US in 1945 didn't have more than ten which could be deployed within the next nine months (someone correct me if you can I'm not sure on this one) so they would be used sparingly. Remember they are also not of the biggest yield, enough to flatten a small city and damage the surrounding area. Most of Eastern Europe is a wasteland anyway, using nukes would just be burning down the rubble and Russian war capacity would be moved East of the Urals and mostly out of range (logistically difficult but not impossible, people tend to move fast when nuclear fire is threatening to burn their arse). Stalin wasn't stupid, if that war broke out, he would be moving production out of range of Allied Bombers.
Also dropping Atomic bombs on entrenched Russian armies is going to present problems whether Allied command knows it or not. Shit, the allies thought atomic sites were safe 48 hours after the bomb went off. Radiation was something that was only beginning to rear it's ugly green head and was not understood. Allied armies would be marching over and near these blast sites and would start suffering from some serious radiation poisoning. It would be a horrific learning experience as thousands of Allies troops move over these sites, they would start dying in droves at worst, at best they would be vomiting their lungs out of their mouths. Depending on windshifts etc. fallout might be raining across Western Europe too and that ain;t going to please France and Britain. Morale breaker!
In short this war is going to be a fucking nightmare. The US might "win" (Whatever that means when you have a devastated Europe, tens of millions of casualties, probably the prelude for WWIV, a crashed, stagnant economy from years of War, riots in the streets of the US from the families of those who's boys were committed to the meat grinder that would be the Eastern front) but it will be at such a high cost globally that the term Pyrrhic victory will be replaced with the term American victory. This ain't gonna be an Ameri-wank, it's gonna be a Global-screw.