Must there be 'tensions between Holocaust historians and Holocaust survivors over facts and interpretation of facts'? Whether or not there must be, there have been such tensions, and Michael Berenbaum discusses some of the reasons why here. Survivors of the death camps emphasize that only the victims can know - from the inside, so to say - what it was like to have suffered what they did, and to have seen what became of those who never returned. At the same time historians emphasize the importance of documentary evidence and how much the survivors could not have known, not having access to the evidence the historians have subsequently acquired. Berenbaum indicates why the apparent opposition in this matter has begun to soften.
It strikes me that, though the enormity of what is under discussion may exacerbate the methodological problems, in principle these may not be specific to the Holocaust. Combatants in war or the civilian victims of war also have an inner experience that isn't available to others, others who only read about war, learn about it second-hand. More generally, the participants in any sort of event know it differently from observers and scholars. At the same time, historians accumulate and study evidence that wasn't open to the participants. I am not a historian, so maybe I'm going further than I should in saying this: but surely the proper study of events of every kind must include taking account of what people say of their direct experience - the importance of oral history is widely acknowledged - while going beyond this, far beyond it, to examine documents, physical remnants, statistical data, and every sort of evidence.