Yes, this is supported. Exchange 2007 and VM Only is NOT supported i believe. (even though you could install Exchange 2007 off box and setup VM-only.)
2000 is end of life at MSFT. Cisco will only ship out 2003 for the message store. (VM only) In UM, you will not get a copy of Exchange 2007, but a copy of Exchange 2003 message store for installation of the Management tools on the Unity server in a UM environment.
Make sense?