You can see which items prevent spawning here wiki / player base [valheim.fandom.com]. Every player built structure prevents spawns on them like wood, stone floors and the like, but not flattened ground.
You could also heighten the area of your base to make it safer or just place the workbenches etc. in places where they can't be seen that easily. Burying them 100% will break them, tho.
And yes, they will keep anything from spawning.