While you certainly can use Scrivener to construct LaTeX, and we have a project template to help in doing so (including instructions on indexing within it), there are other methods you can use that are also provided with the software, that allow for word processing style output, too.
Please read beyond that initial post if you have further questions, this is the main thread for discussion (and I am hence closing this post, as there is no sense in starting all over from scratch). There is also a more feature-rich method that requires a little more setup, discussed here.