I can't speak for FS Global, but PNW completely replaces GEX textures (or any other scenery textures) within its area - you'll see GEX textures outside, and PNW textures inside. The 'border' is very obvious. PNW is also compatible with the UT landclass - again it ignores it and uses its own, but they match quite nicely in terms of roads, rivers, coasts etc.