If it is a Harris built system then this would be correct as any channel can be assigned as a control channel. Remember that any channel in the system that is not the ACTIVE control channel at that time can be used for voice. I think they rotate regularly as well on Harris systems but it has been a while since I followed one.
Motorola built systems typically have a designated Primary control channel (which would be shown as blue) and 1-3 Alternate Control Channels (shown as blue). Motorola systems typically do not use the Alternate for voice channels unless and until all of the voice-ony channels (shown in black text) are busy. If you follow a system with Pro96Com or Unitrunker and watch the hit counts you will see that the Alternate channels have a much lower incidence of use than the the Voice only channels on a Motorola system. On Harris systems the hit counts are more evenly spread out.