Is Substance a good option for creating VR and AR content?

I think it depends on what you want to create.  Substance is a broad toolset and a leader in the game industry where Unity is highly used.  So it depends when you say "Substance" what you're looking for!

Substance Modeler is our modeling and sculpting tool.  You can absolutely use this to create game assets, but note that it doesn't have retopology tools so you'd need to do some work to decimate, retopo, and make the game light enough in terms of size to work for AR/VR which tend to have extreme requirements.

Substance Painter is our primary texturing tool for painting assets and is the industry standard for most painted textures in games and films.   

Designer can be used to create parametric materials which can be used directly in Unity as well as in Painter/Stager.

Stager is a rendering and layout tool, so it could be useful if you want to do some small scene layout or material assignment work before going into Unity, but Unity can do all that layout and material assignment too, so probably not much point.