I think the appendices are usually spoiler free for the book they are found in, at least when it comes to major things, like a character dying. I think that for the most part you should be OK to read it.
But it is true, they mention camps (kings and alliances) that isn't publicized at the beginning of the second book yet.
But no big spoilers. If someone dies halfway through book two, he'll be shown alive in book's two appendix and shown dead in book three, etc.