A reboot is required on the exchange server as that's where the connector will be installed. If it so happens to be the unity server, then a reboot will be required. If subscribers are homed on the exchange server, then Unity will go into UMR mode which is just slightly less distruptive.
Release Notes for Cisco Unity Voice Connector for Microsoft Exchange Release 11.0(2)
http://www.cisco.com/en/US/products/sw/voicesw/ps2237/prod_release_note09186a0080227cf8.html#wp64194
Someone will have to give you details of Unity 2.4(6) and voice connectors.
H. M.