I figured I would add my experience here in case it helps someone.
Adding a new host with a CA-signed certificate to an empty inventory in vCenter seems to give this error, but adding subsequent hosts with certificates signed by the same CA seems to work fine. It looks like there is some linkage that is not being made the first time:
So, if I add the first host to the vCenter using the default self-signed certificates, then swap the certificate for the CA-signed certificate and restart the management agents on the ESXi, I can add subsequent hosts to the vCenter without issue. I really don't know why, but I'll see what I can find out when I get some time.
-Doug