The application Address Book will not be backed up, but you want to back up your address book (your data) anyway which is located in your local Library (/Users/[user name]/Library/Application Support/Address Book to be exact). As long as you back up your whole user library, you are fine. If you want to make sure you have a backup of your address book available, you can make a backup from there (in the File menu).
(The application has nothing to do with your actual data!)