XenDesktop does not connect to vCenter because it is unable to trust the server certificate in use. It usually happens in POC environments where the self-signed server certificate has not been replaced, which is added to the vCenter server during installation, with a certificate signed by a trusted internal/external CA.
When adding a host connection to a vmware server the following error message is displayed:
Cannot-connect-to-the-vCenter-due-to-certificate-error

Additional Resources

Citrix Forum Discussion
VMWare Knowledge Article

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