My admin and I have been having a discussion about putting the vCenter server on a VM or keep it on a physical server on but it on a VM. When we first started using VMware we only had two boxes in the HP and I can't remember precisely what we did but we found ourselves without the ability to manage the environment. We now will soon have four host server with two of them having 128GBs and the other two at 64GB. We will be running about 60 VMs.
It really depends on your needs. We run our VC in a VM, but I hear a lot of people run it as a physical box. If you loose connectivity to the VC server, you can always manage the hosts by directly connecting to them with the client. In the past when we have had VC issues, this is what I have down to remedy the issues. When it comes down to it, it is a personal preference.
Yep, we have this discussion all the time. Some people want to keep the thing that manages their environment completely separate. But in that case you would surely want to have a domain controller and dns servers physical for the same reason.
However, if you make your Virtual Center, DNS and Domain controller virtual then they become more resilient and redundant so surely this would be better. You can protect them with HA and FT potentially.
I would prefer personally to have it as a virtual machine, because its not as if you can't manage the environment if it went down. You can just use the client to individual hosts, and it is less likely to go down as its protected by the features and advantages of being virtual.
Hope this helps?!?