All ICF walls below grade, that have habitable space on one side (basement), must have a waterproofing / dampproofing membrane installed. For walls that do not have habitable space on one side (crawl space, frost walls, etc.) the EPS can be left exposed to the earth. The EPS will not deteriorate when exposed to the earth.
A stud finder typically uses the density of materials to locate studs. The polypropylene (plastic) web material will show up on high quality density stud finders. Note, the webs in Fox Blocks are spaced at 8″ (200 mm) on center and will be continuous vertically on each side of the wall.