I had a quick look at the CommGen run control and the email parameters don't show either CC or BCC. So I figured I'd look at the application package (SCC_COMMGEN) at the email functionality which is in the CommGenEmail Application class under Util, and that code has functionality to get and set the CC & BCC (as its using the MCFOutBoundEmail email functionality in PeopleTools).
However, when you look at the base class SCC_COMMGEN.Model.CommGen, no parameters are passed to set the CC or BCC. So it looks like the functionality is not delivered by default? I also checked out PeopleBooks to see if there's anything about this in there, and it doesn't look like there is.
It looks like it would be relatively straightforward to add CC/BCC functionality as a customisation. Perhaps this would be a good GSC enhancement request?