ITTL there was plenty of evidence before the camps were liberated that Jews and others were being killed, it was the scope that was not truly understood. ITTL it is simply not possible to conceal what has been going on, not just with the Jews but the Poles, Russians, and others who were being enslaved or killed. The presence of a slave labor system including the features of the pre-CW US south or the sugar plantations of the Caribbean simply cannot be concealed. Travelers to "old" Germany (post Anschluß borders) will inevitably see slaves whether as domestic servants or garbage collectors. There will be folks who travel to Ostland, even if only those from Axis aligned countries, and their observations will get out. Furthermore the border between Ostland and the rump USSR is long and somewhat porous, especially for quite some time after the fighting stops. Russian refugees leaking across the border will have tales to tell as well as some hard evidence such as photographs. During the war the story that the Jews were being "relocated" could be sold, but afterwards, especially with Generalplan Ost in swing this won't fly. Furthermore, I expect at some point that the Nazi hierarchy will have its own "mission accomplished" moment where it will declare that all Reichs territory is now Judenfrei/Judenrein. So where did they all go if not anywhere under German control now??
Also, IMHO, Holocaust deniers will be seen as Nazi apologists which puts them in a bad situation. The problem is that being a holocaust denier ITTL is now not just denying that Jews (and who cares about them anyways) were killed by the Nazis by the millions but also millions of Poles, Russians, Ukrainians, etc also killed in one way or another. OTL Holocaust denial can be sold to those who are basically antisemitic, ITTL the killing cast such a wider and bigger net that denial is signing on as a Nazi sympathizer from A to Z.
Also, IMHO, Holocaust deniers will be seen as Nazi apologists which puts them in a bad situation. The problem is that being a holocaust denier ITTL is now not just denying that Jews (and who cares about them anyways) were killed by the Nazis by the millions but also millions of Poles, Russians, Ukrainians, etc also killed in one way or another. OTL Holocaust denial can be sold to those who are basically antisemitic, ITTL the killing cast such a wider and bigger net that denial is signing on as a Nazi sympathizer from A to Z.