Hello Ken, did you figure this one out? I'm experiencing the same problem right now on ESXi and vCenter 6.7 on a Nimble array. The Vvol container is successfully advertised to vCenter and I can connect it to the hosts, but then the connection fails and no protocol endpoints are displayed.
The certificate the SAN presents to vCenter appears to use FQDN, but the VASA provider is registered with IP address. I'm wondering if the mismatch is confusing the vvold service.