Is there anyone know ghettoVCB support Incremental or Differential backup for VMs or not? Can we modify the script to support Incremental or Differential Backup?
No, ghettoVCB only supports full backups. It is a very simplistic solution catered to supporting free ESXi.
If you're looking for more advanced backup capabilities such as incremental backups, you'll want to take a look at some of the commercial backup/recovery solutions out there including VMware.