Sure, you can use FC HBA's or iSCSI to connect to external storage. vSAN supports this, note vSAN itself will the normal vSAN network.
To connect / migrate the virtual machines from iSCSI/FC/NFS to vSAN if they are on different cluster:
Note: Please take care of CPU affinity rules and resource pools and proceed with the below plan of action.
- Present current SAN storage to new ESXi vSAN Hosts.
- Shutdown virtual machine and remove it from Inventory on old cluster.
- Re-register the virtual machine on a new vSAN host cluster.
- Using storage vMotion migrate the VMs to vSAN.
- After migrating all virtual machines, un-present vSAN LUN's.
Please mark this as correct if this answers and helps you .