As long as you already have them checked out/downloaded, yes! Some notes:
Cloud Library App - open each book once before leaving the connection zone to ensure it downloaded. If the app continues to put a "no server connection" bar over your book, put the device into airplane mode while reading (stops app from trying to reconnect to servers).
Freading, Enki - once your book has downloaded to the app, nothing special is required, though we do like to open the book at least once to double-check it has downloaded before leaving the wifi area.
Please note that BookFlix & Unite for Literacy are in-browser only, and require an internet connection.