You cannot configure the option for Agents not to chat with each other. As a work around, you could remove the chat button from all CAD clients, this way, only Supervisors can initiate a chat with them.
If you saw a demo of a "buddy list," then you probably saw UCCX integrated with CUPS, in which case, you can configure groups of SME's and assign them to teams. Also, if an Agent logs out of CAD, and then into CUPC, they can build their own personal contacts, so when they sign back into CAD, they see that list as well.