There isn't really any criterion or 'requirement' for FOD other than try to avoid it if possible!
When hovering overland, the occasional placcy bag etc is just an operating hazard that won't go away. SAR crews usually do a thorough recce of the operating area wherever time permits and will discuss any potential nasties, same for any military crew really.
At the end of the day if a casualty needs picking up in the middle of a rubbish tip then there are only so many ways to effect a rescue. The crew will operate to keep risk to the minimum but it will never go away completely.
Most helos these days have some sort of intake filter so FOD isn't quite the issue it is for a jet. Unless you get something in the tailrotor of course, thats usually terminal, hence flying pay I suppose.