Without having the SSL thumbprint of an ESX host, it is hard to add a ESX host.
Here a simplyfied script to retrieve the SSL thumbprint:

This skript returns the SSL thumbprint for further use, e.g add host to cluster.
It is only a simple example, but essential for automation host tasks.
To add a host to a cluster without having SSL thumbprint you can use a modified version of "Add host to cluster":

or import the package below wich contains the modified workflow.
Fell free to leave comments.
Regards, Andreas