You must include your own bar code for your one-piece cover. Unlike separate front and back covers, your ISBN bar code will not be automatically added to your one-piece cover. It is up to you to add every element you want to appear on your one-piece cover, as this type of cover allows for total customization. For more info on generating bar codes, see http://www.tux.org/~milgram/bookland/.
See Also: Will Lulu add a barcode to my cover?