Of course he is aware of her background. How else would he have read the quote? In fact, I would like to know when he did read her material. That speaks volumes to me.
Many people have only read her expurgated diaries (as I have), and have no idea that the unexpurgated diaries even exist. I only just recently found out that she committed incest with her father, committed bigamy, etc. It was a great lie perpetrated by her publishers to deliberately leave out all the sordid details. We may have thought the details were left out only for the sake of space. I mean, condensing decades of material into 7 volumes. What we didn't know was that they were entirely crafting the image of Anais Nin that they presented to the public. I will never again read an abbreviated or expurgated diary. I have no way of knowing whether Rick Warren has read the expurgated or unexpurgated version of her diary, or which others books of hers he has read, or how he happened to find the quote he used. At this point, I don't even know which quote he used.