Media doesn't 'exist' within BackupExec until BE places a header file on it with the on-tape media label. This only occurs when the tape is erased, or when the tape is selected to be used for a backup. In tape libraries, BE will automatically assign the barcode value and perform a label operation when a inventory is performed. This is not done in a stand-alone drive without a barcode system, because BE wants to give you the option of your own unique on-tape label or if BE should generate one.
So, an inventory should be the minimum sufficent user action in your environment. BE will automatically assign your blank media a label upon the first backup job and it will then show up in the Media Tab.