Is space/vacuum a substance? Clear cut divisions and definitions dont truly exist, they are created by humans for means of convinence. Everything is connected in nature because everything relies on something else for its existance, ive always seen the division between being and nonbeing more of a scale you can move up and down on rather than one or the other. On the furthest end of the scale representing being you get experience, life and on the other end you get complete nonexistance probably what most of us associate with death. You dont get one without the other because they both have to exist to imply one another. That being said space is something we can observe and although its quite barren compared to the richness of our planet and lives it still has properties, so to wrap this all up my conclusion would be that space is on the further end of the scale towards nonbeing than being but not true nonbeing because if that were the case it would be completely invisible to us.