During a new lab deployment of VCF 5.0 i ran in to an small issue running the validation.

I deployed the hosts up front and made them available and unique before the validation. ran the following command to regenerate the certs and restart the services:

/sbin/generate-certificates
/etc/init.d/hostd restart && /etc/init.d/vpxa restart

Next i wanted to see what Common Name (CN) was on the certificate:

As you can see the Common Name (CN) contains only the hostname.

Next i changed the hostname on the ESXi hosts to have the complete FQDN.

Checked the hostname on the cli, and regenerated the certificates again:

After the regeneration of the certificate on the Host, you have to restart the services:

/etc/init.d/hostd restart && /etc/init.d/vpxa restart

Check the Certificate in the browser and now the Common Name had the FQDN in it, and the validation finished successfully.