Amazon recently banned the sale of so-called 'holocaust denier' books (on March 8), seems that youtube is about to follow suit.
1984 is in very large part about historical revisionism. If anything, the term "holocaust denier" is the opposite of Orwellian, in that it specifically stigmatizes revisionism.
You could debate some of the numbers - was it at the lower end of the estimate or the higher end, but pretending that there is any legitimate reason to claim that the holocaust didn't happen is denying fact.