Export them to CSV instead, much easier...
e.g.
Get-WMIObject Win32_QuickFixEngineering -ComputerName "Server2" | Select-Object HotFixID | Export-CSV "Server2.csv"
Then you can do this:
$Server1 = Import-CSV "Server1.csv"
$Server2 = Import-CSV "Server2.csv"
And finally you're back to compare object again :)
Chris