Having a VLAN for storage seems like it’s the “best practice,” but since both servers still need to be accessible outside the VLAN, the only benefit I can see is limiting broadcast traffic, and as far as I know (correct me if I’m wrong), SMB/NFS/iSCSI are all unicast.
Having a VLAN for storage in your case is totally pointless. The traffic is still going to the same switch with added overhead of having to deal with VLAN tags and whatnot.