The following powershell script can be used to automatically get a list of all powered-on Ubuntu VMs, along with their IP addresses, from a VCenter server.
Connect-VIServer myServer.tld
(Get-VM).where{$_.PowerState -eq "PoweredOn" -and $_.ExtensionData.Guest.GuestFullName -match "Ubuntu"} | Select -Property Name, @{N="IP Address";E={$_.ExtensionData.Guest.IpAddress}}