Not exactly sure what you mean by the cluster UUID?
An ESXi node has a UUID, that one you can get as follows
foreach($cluster in Get-Cluster){
Get-VMHost -Location $cluster |
Select @{N='Cluster';E={$cluster.Name}},
Name,
@{N='UUID';E={$_.ExtensionData.Hardware.SystemInfo.Uuid}}
}
Or do you mean the UID?
Get-Cluster | Select Name,Uid