We are moving from older servers to newer servers and I have built the new cluster using the same vCenter. The storage is different and the old cluster does not have access to it so I am shutting down the existing VMs and migrating them. What can I do for vCenter? I am guessing the answer would be "build a new vCenter appliance" or add the storage of the new cluster to the old cluster but was hoping there was another way to do it that I might have missed.
You can try use the enhanced vMotion that will allow you migrate VMs to different hosts event if there is no shared storage between the hosts... BUT you will need to use the vSphere Web Client.
Options - other than what you already mentioned - depend on the licensed vSphere edition and the old ESXi version you are running. If you are running vSphere Esentials Plus or better, and there's an option to upgrade one of the old hosts to ESXi 5.5, you will be able to live migrate the vCenter Server from the old to the new storage.
Also I am not sure if the enhanced vMotion will work as our vMotion network is on the same network as our Managment and is not separated. I was told a few years back it wasn't necessary anymore to separate vMotion traffic if we are in a small environment (3 hosts, 50 VMs). Not sure if this has changed or not?
is there a way that you can add a shared LUN between the clusters? that would be the easiest way. otherwise, shut it down, move the files manually and start back up. A bit messy, but doable.
It may not be necessary to separate the vMotion network from production, but it is highly recommended, not only to avoid possible networking issues, but also for security reasons because vMotion traffic is unencrypted. Anyway, with all hosts already on v5.5, you should be able to live migrate the vCenter Server using the Web Client. If the network configuration isn't setup according to the requirements you will receive an error/warning message, so just try it.