When you install VMware Update Manager Update 2 on your Virtual Center Server and then you install the plugin from your VI Client ánd you have the VI Toolkit installed, you have the option to install the Powershell extensions for Update Manager. They are still in beta though, so only use them on your testing environment.
You have to load the extensions in order to be able to use them. This is how:
In order to list all new cmdlets in this snapin, try this:
Get-Command -PSSnapIn VMware.VumAutomation
That should get you on your way of exploring this great addition to the VI Toolkit. Here’s a nice one-liner to keep you busy:
(Get-Compliance (Get-VMHost (Read-Host “ESX Server”))).NotCompliantUpdates