Are you able to use one vCenter server to manage both servers and desktops? One cluster of ESX hosts contains server workloads and the other cluster of ESX hosts contains Citrix desktops. What would be the licensing needed. Thank you.
If you are using Citrix VDI, and simply running those desktops on a Windows OS, then yes, you can run them in a single vCenter. However, SSO and vCenter are critical components in a VDI environment. If either is unavailable, virtual desktops will not be handed out. Only sessions which were already active will remain so. So as opposed to an enterprise environment, where manageability is impacted by the loss of SSO or vCenter, in a VDI enviornment the impact is loss of servuce to your desktop users.
So yes, you can, but you probably shouldn't. I would recommend having a separate environment on separate hardware. Depending on the size of your VDI environment, I would also probably use external PSC's and 2 vCenters with Enhanced Linked Mode.
The answer to the question is yes!
2 vCenters means two points of failure! Let's not forget that HA will restart vCenter in the event of hardware failure.
While it is true that desktop availability may be affected by/if vCenter is unavailable, how can we virtualize any mission-critical application on vSphere if we need to maintain separate vCenter instances just to run VDI? Besides, I am pretty sure that users can continue to connect to desktops after they have been provisioned, even when vCenter is offline. After all, the Connection Server is only a broker, the piece of the puzzle that really interacts with vCenter is Composer!
There is a licensing argument in favor of running separate Clusters for Horizon View, but separate vCenters seems excessive and wasteful.