And then you have Mother Theresa types, but avoiding two extremes, what manner of Christians Rome overall fosters is an issue.
Stalin was a Russian Orthodox seminarian before declaring himself an atheist—he later had thousands of priests harassed, imprisoned, or killed. Hitler was baptized Catholic, but fell away in a pretty big way: He had his political party specifically condemned by the Pope and murdered thousands of priests and nuns, and millions of Catholic laymen.
I have heard that Hitler was a Catholic altar boy in his youth. He certainly did not die as a public adherent to Catholicism. His life suggests that his access to heaven was no better than Stalin's and for largely similar reasons of mass murder. Hitler also added to a mountain of crimes and sins, death by suicide, putting a gun in his mouth and blowing his brains out.
We Catholics believe that if a person with however vile a track record accepts a grace of final repentance, makes an act of perfect contrition (not out of fear of hell but for simply offending God and thus rejecting His love), then his sins may be forgiven by God. Many of Hitler's public sins were of a sort in which one such sin would excommunicate him latae sententiae. He did not have a lot of time between pulling the trigger and death and he would have been distracted by the pain. God certainly knows as does Hitler.
Adolf Hitler was not an altar boy.