As coolsport00 has mentioned, if you do have HA, then the Vcenter issues might not be that great as long as you set the HA to automatically migrate your Vcenter VM over to the other host during failure time. Of course, the Vcenter VM must be setup properly in this scenerio.
Of course, during maintainence time, just manually migrate the Vcenter VM to the other host while updating. This way, it keeps the progress smooth with interruption.
So .. a Vcenter VM is okay. However, IMO, i would still prefer a physical box just to seperate the vcenter and the VM cluster, since VMware design it that way. It is however totally up to your comfort level.
