Yes, providing there are no chemicals the soil should be fine, it`s usually best to add some playsand (it`s trial and error, but start around 75 to 25% soil to sand mix). It should be moist, not wet and tamped down very firmly so it will hold a burrow (18 to 24 inches deep is o.k).
Having a deep substrate will in itself help maintain a good humidity range (keeping the monitor hydrated), if you cover with a layer of (non-toxic) leaves or similar it will help stop the soil drying out too quickly.