The "stack" the OP refers to is the Stanfield/Casa Grande (TFD/KCGZ) stack used in the practice area south of Phoenix. I've done a number of IFR flights to Casa Grande and Albuquerque Center will often times clear you in for the ILS approach while at the same time there's anywhere from three to five other aircraft all operating VFR circling over the VOR or on various stages of the approaches (ILS/LOC, VOR, and GPS for runway 5). About a month ago I had center clear me for the approach with a descent to 4000ft while at the same time there were VFR aircraft in the published holding pattern over the VOR directly in the final approach course at 3500, 4000, and 4500 ft. Had I not been monitoring CTAF on COM2 I'm pretty sure my student would have blindly followed center's instructions and even if we managed to avoid the traffic holding at 4000 we probably would have descended on top of the guy at 3500 as he shot the practice approach.
That being said, center around here will usually tell you "vectors for visual" on most VFR days and won't give you an instrument approach unless it's less than VFR weather or you specifically request it.