Do you have Data Protector installed?
If so, have you done the VMware integration?
When backing up ESX virtual machines, you can back them all up by backing up the Virtual Center, or you can backup the ESX clients individually
To backup over fiber, your Virtual Center or the ESX clients have to be able to see the tape library or d2d device. When creating the device, you include the vCenter machine or ESX clients as hostnames. When creating the backup specification, use the option 'Use Preferred Host', so that whne backup starts, disk agent and media agent are the same hostname
Remember, this is only of you are using Data Protector
I am not able to answer the question about 'what system can be used as a backup host', that is more of a VMware issue