First of all you need to be licensed for Unified Messagaing in order to allow access to VM via outlook. Second of all you need to be integrated with production AD and Exchange.
Unity 5.0 allows you to mix licenses, UM and VMO where the setting is controlled in COS.
For the users that need UM you simply import the users from AD/Exchange, and for users with VMO only you create new "dummy" accounts with new Exchange mailboxes.
HTH,
Chris