You must not confuse IFR with IMC. Instrument Flight Rules that come in to effect when VFR can not be followed or where certain airspace is designated as permanent IFR. So you can be visual when following IFR. As it happens, most circuits are, not surprisingly, visual affairs and flown under whatever rules apply at the time. And to be honest, most of trainers I know firstly wouldn't have a clue and the rest wouldn't care - all they want is appropriate weather to fly their detail. Lastly, the guys above have described the mechanics pretty well.