The following block works:
$customDLL = "C:\Users\xxxxxxxx\Downloads\NimbusAPI.dll"
$assembly = [Reflection.Assembly]::LoadFrom($customDll)
Add-Type -Path $customDll
$session = New-Object Nimsoft.NimBUS.Messaging.NimbusSession
Trying to get a list of hubs, but not working.....doesn't seem to recognize the callback function
$hub = New-Object Nimsoft.NimBUS.Probe.Callback("hub", "gethubs")