"if they endorse Finklestein for his denial of the holocaust"

I haven't read the book - but from what has been written about it here it does not sound as if it involves "denial of the holocaust".

If, as I understand it, his point is that the historical fact of the holocaust has been exploited for political purposes, and that the genocide and mass killing carried out by the Nazis against groups in addition to Jews has not been given adequate attention, that is very different from "holocaust denial".

I just googled for reviews of the book and the one that came up top was from The Economist, with a quote from "Raul Hilberg, most distinguished historian on the Nazi holocaust and member of the American Academy of Arts and Sciences":

"When I read Finkelstein's book, The Holocaust Industry , at the time of its appearance, I was in the middle of my own investigations of these matters, and I came to the conclusion that he was on the right track....I would now say in retrospect that he was actually conservative, moderate and that his conclusions are trustworthy."