I have exactly same issue. When I configure SMB share as back up target, it says "SMB location is unsupported".
If SMB share is a Windows based SMB share, it worked. But for some security reason of customer, Windows based SMB share is no longer possible in the environment. So an SMB share from NAS storage was provisioned. Then I started getting the error "SMB location is unsupported". Is Windows based SMB share only supported? I could not find any VMware document about that.