Yes, you would use a simple brush like a wall over the entrances to the spawn covered in the "nodraw" material and tie it to the entity: func_clip_vphysics This would allow everything but physics objects to pass. If you do want certain physics objects to pass, there is an option for a filter, so you could set it to allow anything else that is a prop_physics in the level to pass.

That would mean giving all those props a common identity either through a second filter, or just naming them all the same thing. The only drawback is, I don't know of a way to allow thrown weapons or ammo to pass and not grenades, cause their all considered prop_physics, and there's no way of labeling them cause they spawn with the player each time.