Technically, I think your proxy is what needs to be able to see the LUNS. I run a Windows MA and that also has the VMware proxy installed. It also needs to be able to connect to the vcenter.
If your proxy is not on your MA, the path between the MA and the Proxy will wind up being some sort of a LAN connection rather than a FC connection, I think.
In my environment, SAN mode backups gave me a huge performance boost on large VMs. It wasn't because the network was faster, though, it was because that protocol for interpreting the blocks of data is just better optimized than using the protocol that goes through a VMware host over the regular network link. I know this because both networks were 1gigabit iSCSI when I first set it up and backups of VMs greater than 3TB that would otherwise take 8 hours started taking only 3 hours. From my point of view it looks like the API for SAN mode was just better written than the NBD protocol. I believe the APIs for all 3 modes were written by VMware so I don't know why that is.
(I've heard that HotAdd mode is also nice but since I write tapes I use a physical MA rather than a virtual MA.)
More info is here: https://documentation.commvault.com/commvault/v11/article?p=32037.htm