Yes - I remember reading the Prologue before I started FOTR, but no - it didn't
spoil it for me at all. Even though I had read The Hobbit, I still did
not know who most of the characters mentioed in the Prologue were, nor how
important they'd be to the story. All it did was give me a warm-fuzzy
feeling that many of the characters would survive, go on to live long and
productive lives, and write down the history that I was about to read.
I suspect it would be the same for any first time reader who's had no exposure
to the story
yet.
"I don't suffer from insanity...I enjoy every minute of it!"