What is the difference between OPC and GE CCM protocol?

The CCM Protocol is specifically for communicating to the PLCs.

OPC is a protocol for sharing data from application to another.  This is similar to the concept of Microsoft's DDE.

A common architecture for using OPC and CCM in a system together would be:

PLC ⇔ CCM Protocol ⇔ Your App. ⇔ OPC Protocol ⇔ Other App.