Can I use scenery packages from Microsoft Flight Simulator?
No. The formats are completely different. But… There is a scenery plugin available that loads MSFS scenery objects and custom textures into X-Plane. This does not give you complete MSFS scenery in X-Plane, but it does populate the somewhat barren X-Plane default scenery with all the MSFS objects. This plugin will work with versions of X-Plane 6.70 and later.