As far as I know, when users installing VMware vSphere Hypervisor (free version) they can use it in three way, for 60 days in trial period with full feature, they can enter their free license or they can use the license they bought which means more feature would be available for use.
For checking different edition check these links: (Compare vSphere Kits and Compare vSphere Editions).
I’m using free edition right now and this is my license below:
In the other hand VMware vCenter can be used in trial version for testing all features or with the license users bought.
When users buying license for their environment for the first time, they will hose between available editions and kits which suite their need best.
The final result would be the same some how, they will busy licenses for VMware vCenter and Hosts (ESX or ESXi).
Until now, theres nothing new in these notes I wrote here, lets check the VMware vSphere Hypervisor.
Is it possible to centrally manage VMware vSphere Hypervisor? as the chart says, NO also check this link (this link is for VI3) and search for “Other useful ESXi facts” in it, the first paragraph after it said:
The basic version of ESXi can not be managed by VirtualCenter, as it does not include a VirtualCenter agent.
Is it mean that we can’t add VMware vSphere Hypervisor to our VMware vCenter? NO
Well, as following screenshots will show, YES, you can add free licensed hosts to your vCenter server when you are using VMware vSphere (at least I checked this with 4.1), but in this case you will only have very limited management capability, in this case instead of opening four vSphere Client for four servers for managing them separately, you can use on client connected to your vCenter.
But again, you will not have any feature of ESXi or ESX with license, you can just manage them centrally, thats all.
You may think there is no way or no reason for having vCenter server and free licensed hosts together in the same place, but always there is exception and cases which need more flexibility than the others, like this one.