If you just do a flat file backup of the BKF files, you will have to restore the BKF files to disk, then inventory and catalog before you can restore And no, you must copy all of the catalog files associated with the job(s) that you want to take offsite
If, however, yuo do a Duplicate job, BackupExec will create a copy of the backup set(s) on the tape(s) and you can restore directly from tape.