Kind of got some bad news for you
DAG backups are not supported by the VMware agent, which means you cannot use the VMware SAN Transport
non VMware backups need remote agents installed on every Exchange server that owns a copy of a mailbox database within the DAG (and possibly the Exchange CAS as well). Communication with these remote agents will be over LAN protocols (not storage protocols) and will need a route to each part of the DAG, access to the BE required TCI/IP ports (Port 10000 etc) and name resolution working to all servers in the DAG
If SAN Transport in VMware is not an option then there are two other options for BE to backup over SAN.
1) Make every server containing the data into a media server and then make sure your backup targets are directly connected to each media server (extra media server licenses needed, and possibly SSO as well if you want to share a library for backup data storage) - you can't really do thius as your Exchange servers are virtualized.
2) use ADBO "off host",. This needs licesninses and for the hardware storage devices to be on the compatibility list for this option and to be honest I am not sure if this can be DAG aware either. If it is DAG aware then the storage on every node in the dag will probably have to be avaiable in some way to the media server and some LAN requests still have to be made, so all the connectivity points already made will be needed. - Again you cannot do this as your servers are virtualized
I think you will have to drop your backup over SAN (iSCSI) option and just use standard remote agent (GRT enabled) backups of Exchange over LAN - possibly using a backup LAN by adding extra network cards
EDIT: just realized not answered part of your question.
VMware file server backups do not need to talk directlty to anything within the guest server to run the backup, even for GRT capability of individual files. When it comes to a restore though unless you restore to the media server and manually copy then to restore an individual files would require LAN access from media server into the virtual server itself.
Exchange GRT backups using VMware (as long as not DAG) do need to talk to an agent inside the VM to gather the metadata needed to restore Exchange, as such they cannot be on a segregated network (VLAN) but must have comms.
Of course because of your DAG you can only do DR (Exchange GRT disabled) backups of your VM's containing Exchange using the VMware agent and will then have to do Agent based Exchange GRT backups of the mailboxes (over the LAN) to have individual e-mail restore capability.
