A.H. regarded the Russians/Slavs as 'subhumans' and the USSR was his primary enemy ie. he considered Bolshevism a 'jewish disease.' German and Polish Nationalist forces even allowed over 70,000 Russian prisoners to freeze to death and die of starvation on abandoned cattle cars... It was really premeditate savageness ie. part of the holocaust.
Also, if one reads the doctrine of how Operation Barbarassa was to be carried out, one soon realises that A.H. from the very beginning had the agenda of being extremely brutal. In fact, A.H.
had even woo'ed the pope into a plan to destroy the Russian/Eastern Orthodox church...and to replace it ostensibly/finally with the Roman Catholic church... Also, Russia was viewed by A.H. as his 'lebensraum' and A.H. argueably was as obsessed with anti-Russian sentiments as he was with antisemitism ie. A.H. once exclaimed 'When it comes to Russia, I just cannot help myself...' and he constantly uses the words bolshevik and jew as interchangeable words...ie. he would give speeches on building the reich as a bulwark against bolshevism which he considered a jewish disease, and he also considered the Russian people as tainted slavs...who would in essence be the slaves of the new reich.
A.H. and other top nazis also seemed to believe that the West was really deep down on their side in the fascist war against Russia ie.Rudolf Hess' mysterious flight to England has been resonably speculated as an attempt to woo Britain into a peace with Germany so as to be an ally in a war against the USSR...and for many decades this was an issue of dispute/mistrust between Russian/British/US officials in regard to Hess and his long confinement...
Allied POW's from other countries were at greater risk if they were identified as jewish...but one thing that tended to save them - was that unlike Russia - the West had signed the 1920's Geneva Convention, so a captured allied soldier of the West
was ikely to be treated better by the Germans. I would emphasize the word 'likely' because a lot would of course depend on the circumstances of being captured. Russians also tended to be captured in masses...in greater numbers...and subject to sweeping harsher conditions...of combat ie. subject to death march conditions ...