when looking for VMs or other types of objects that are in say a cluster and on a specific datastore in that cluster get-vm -location and -datastore can return a AND or OR list though AND is likely more helpful most with VMs.
VMware filters work on an 'and' basis. Luc has given the correct methodology for using PowerShell to do the 'or'.
Aren't those basic operations that can easily be done with PowerShell?
$vmDS = Get-VM -Datastore MyDatastore
$vmCluster = Get-VM -Location (Get-Cluster -Name MyCluster)
# Union (OR)
$vmDS + $vmCluster | Select -Unique
# Intersection (AND)
$vmDS | where{$vmCluster.Name -contains $_.Name}