Can't comment on what requirements you need to meet on the OCS side, but yes - its definitely possible what you are trying to do. Basically there is a TAPI session created between the OCS and the CME. Thus, if any user who is logged into the OCS server and right click and press Dial. At that point, the OCS instructs the CME, to actually place a call.
The CME configuration is pretty straight forward..
There is also another product called "Unified Call Connector" which also acts the same way, and functions similarly..