Can you try it with the Vamp simple host (vamp-simple-host) in the SDK? (There is a binary version of the host available in the SDK downloads, if you don't have or want to build one.)
If your Vamp plugin DLL is in the Vamp path, then just running "vamp-simple-host -l" (that's a lower-case "l", for "list") should list its name and description (among any other plugins that are also installed).
Chris