Both, actually.
Search & Rescue, Cadet Orientation, Counter Drug, Photo Recon, etc. are obviously VFR only. Transport Missions and aircraft repositioning can be done IFR. However, to do an IFR flight on a CAP mission, one needs more than the Instrument rating. I can't remember all of the hopes one has to jump through, but it at least involves a checkride with a CAP Instructor Pilot.