May I ask what do you mean under "CC category"? AFAIK there are only four standard (out-of-box) file categories in the Vault: Base, Office, Standard and Design (free translation from Russian).
Let assume you mean some custom file category .... which has its own custom categorizing rule, right?
"The only way to separate CC files from normal files is by the Inventor "Is Content" property."
I'm trying to reproduce your scenario, and I don't see the possibility to use "Is Content" property in categorising rule* section. Here "Initial Release Date" is followed by "Latest Release Revision"...no "Is Content" property available. So what is a plan to use the property for file categorizing?
* Vault Profesional 2012 upd1
File Rules -> New -> OK -> Property