If you don't have vcenter no issue .
ESXi is the hypervisor, where you create and run virtual machines and virtual appliances And vCenter Server is the service through which you manage multiple ESXi hosts connected in a network and pool host resources.
So you can deploy your webex vm in your esxi without any issue .
Please follow this youtube link for installation and initial configuration of CWMS
https://youtu.be/DaGoa7ujW6o