When you run that command/script manually from the vMA, do you do in the vifathpass authenticated context?
Seems like you don't pass the login info of your host to the vifs command.
Is "vifs -g '[datastore1] log/ghettoVCB-backup.log' /tmp/backup.log" the exact command from your script? Try supplying the credentials via sessionfile/configfile or with the --server, --username, and --password options.