Unity currently supports only Exchange 5.5, 2000, 2003 and Domino R5 and R6. No unified messaging support for Groupwise is available.
You can use the Unity Inbox which is a web based voice mail viewer to give some level of integration to other mail servers, including Groupwise. When new messages arrives for a user an email goes out to their mailbox (in this case their Groupwise mailbox) that includes a link to their web based inbox viewer which lets them get their voice mail from their desktop.
You can read more about it in the "setting up client appliations" section of the administration guide - the admin guide for Unity 4.0(4) can be found here:
http://www.cisco.com/en/US/products/sw/voicesw/ps2237/products_administration_guide_book09186a00801ba3db.html
