I don't know what your AIP says about it but it occurs to me that, if the chart shows a mandatory minimum altitude of 4000FT prior to the IAP, the pilot must observe that. If it does not show that as a mandatory altitude, a pilot would seem to be at liberty to descend to your MVA of 3000FT for a more convenient start to the ILS approach.
If the procedure is predicated on separating departing traffic from arriving traffic, I would have to say that it would be up to the Air Traffic Controller to tell the pilot of an arriving flight not to descend below 4000FT until passing the IAP, due traffic.
As I said at the outset, your AIP might say something different but, in absence of that, the above is my interpretation. Maybe there are others who can comment in the next few days?