lol, before i went organic soil I used recyeld tire mulch as a hydro mediu,. It worked fine. I did not finish with it, went to rockwool. It did smell, but ti was recycled. hehe. jk
Howver rubber mulch around your plats would be cool. It would keep the sun off the soil. Keeping the bacteria and mycrobes alive better. It would prevent soil evap. I would not wick.
the grass clipping sounded like a topdressing scheme. lol. Ise guanos for that, and wow.
IDK, if the rubber does not leech chem then it would be awesome. Also keep bugs out.