The mem.swapused.average counter is only for hostsystems afaik.
You could use the mem.swapped.average, something like this:
$start= (Get-Date).AddDays(-1)$metric="mem.swapped.average"
$entities=Get-VMGet-Stat-Entity$entities-Stat$metric-Start$start|
Group-Object-Property {$_.Entity.Name} |%{ New-ObjectPSObject-Property@{ Name=$_.Name
AvgSwappedKB=$_.Group|Measure-Object-PropertyValue-Average|Select-ExpandPropertyAverage } }