There are no issues migrating book files and documents from CS6 to CC other than the fact that both will be converted to the CC internal format.
In general, it's a good idea when documents are converted to Save As over the existing files after conversion. INDD files accumulated internal cruft after multiple edits, and can start to behave unpredictably after conversion. If you do run into any weirdnesses, export as IDML, then recreate the documents and save over the originals, then update the book file.
If you're moving from CS6 to CC, I would suggest you hold off until after the June 18 announcement by Adobe. I can't say more than that right now, but since we're so close to the date I think there's no harm in saying that you'll be pleased you waited. :)