My question would be WHAT book about the Holocaust? Is it something people may have already read or touched upon in school that they may not want to reread or feel like they're reading something similar (ex: lots of people read The Diary of Anne Frank and/or Night by Elie Wiesel), or are you looking to read something like a full on history book?

Personally I would want to avoid something really history-heavy themed if it was for a book club, but would be interested in something that may offer a new perspective or structure - something like Markus Zusak's The Book Thief or Art Spiegelman's MAUS (the latter of which has been recently challenged AND offers the new perspective and structure of the graphic novel format)

As for the thematics, there's nothing wrong with selecting something with difficult topics or themes. It also begs the question of what is the "vibe" of your book club? Are they looking for something specific like new releases? romance? maybe look at the previous selections and see what you can discern.