otl people were aware of mass killings of jews in the holocaust by bullets in 1941; churchill referred to it in a speech in the house of commons. id think that even if the camps are covered up it would still be widely known that germany committed mass murder of jewsThinking more on this...
It's a VERY grim thought, but how sure are we that the Holocaust is actually well-documented TTL? For one, given the theme of "shit goes very wrong but America still wins", I worry Germany might be more successful in covering it up before their surrender. For another, there have been repeated mentions of mainland European archives getting destroyed- which many of us suspect to be due to a post-WW2 nuclear exchange. Aside from it potentially destroying much of what holocaust documentation was made, I think the demographic damage done by the holocaust could get conflated with that done by the exchange.
Suppose that Nazi Germany relatively openly herds the jews and other 'undesirables' into ghettos, but manages to cover up most of the extermination camps (and due to political fuckery, what remains is mostly captured by Soviets that don't share it with the west). Then World War 3 happens, the Polish inner cities get vaporized by canned sunshine along with demographics records. A historian looking at it much later sees 'large jewish population referred to in historical sources -> Nazis herding jews into city ghettos -> ????? -> nukes fly-> not many jews in the modern day.' What conclusions might they draw?
Then again, I might be vastly overestimating the extent to which Germany would be able to cover the Holocaust up.