This was covered in much detail in Morris' biography. He apparently said it but may have been referring to the fact that he was among the first in America to see the movie and still footage of the camps' liberation. He was undoubtedly talking about his emotional reaction to the images and may perhaps have gotten a little hyperbolic. After all, he knew he hadn't really been there and so did the people he was talking to, so a real attempt to deceive seems unlikely.
Besides the fact that Ronald Reagan was an honest, ethical man not given to lying, it goes without saying, he wouldn't tell a huge whopper, easily disproven, to two separate men, on two separate occasions, and certainly not in the White House he so honored.
But wait! We've established neither Reagan nor Hitchens lie, that they are honest men, so how to explain this? Easy as pie with google.com.
Here's the straight skinny, at least as reported by "The Washington Monthly"...not a conservative publication!
"In November 1983, Reagan told visiting Israeli Prime Minister Yitzhak Shamir that he had served as a photographer in a U.S. Army unit assigned to film Nazi death camps. He repeated the story to Simon Wiesenthal the following February. Reagan never visited or filmed a concentration camp; he spent World War II in Hollywood, making training films with the First Motion Picture Unit of the Army Air Corps"
http://www.washingtonmonthly.com/features/2003/0309.mendacity-index.html
It's so obvious to me that this was a simple misunderstanding, most likely a translation snafu, with no self-serving mischief, (on Reagan's part), involved at all. First of all, Reagan wasn't that kind of man, and there's no other occasion (I know of), where he bragged about, or invented accomplishments. And secondly, Reagan wasn't a photographer in his military unit. He acted in army training films, he produced them, and he was the unit's personnel officer.
I can imagine Reagan was looking to seek something in common with these two Jewish men, I can imagine he would have told them his unit was the one assigned to film the concentration camp atrocities, and I can see how easy it was for them to repeat that and have it twisted by those eager to mock President Reagan. Hitchens would have heard that mocking version of the truth and believed it to be true.
Case closed, for me, but how bout some interesting info?
Ronald Reagan - Captain, US Army Air Corps. Because of a severe hearing loss, he was not allowed any flying duties. However, he appeared in training films. Prior to the war, he was a cavalry officer in the Nebraska National Guard. but for Reagan's complete, and I mean COMPLETE military record, go here:
http://www.jodavidsmeyer.com/combat/military/actors_in_wwii.html
And for a wonderful history of "Hollywood's Army", (Reagan's unit), go here:
http://www.wpafb.af.mil/museum/history/wwii/rr.htm