To take a backup of your database, just install the oracle agent for netbackup on your VM, like you would on a physical server.
For best performance, use a separate machine as Netbackup server, and connect the drive to it.
Netbackup will connect to the agent on your oracle VMs and back them up over the network.
Using a VM as backup server could work as well, but you'll have to configure the VM to use the backup device (SCSI i assume) connected to your ESX host, and it cannot be shared between VMs.
Last time I checked, this setup was only supported using an Adaptec SCSI controller to connect the device.
I tried this once, and it worked, but performance was considerably lower than having a dedicated backup server with the drive physically attached.
If you want to use VCB, i recommend putting the Virtual Disk containing the DB in independent mode, so it will not be snapshotted; and only using VCB in fullvm mode for system disk.
You could experiment with adding a separate Backup VMDK to your VM, using Oracles backup mechanism to dump a database backup to this disk, and including that in your VCB backup.
This way you can use the advantage of VCB (speed, no network affection) and be sure you get a consistent backup of the database.
I have no idea on the difference in speed between this last setup and using the agent over the network, though, because the total backup time in the latter case would include first the dump, and then the VCB backup.
