You can always tie plants to the coral. I know my girls would get themselves pretzeled into the coral somehow.
I'm pretty sure coral is all minerals, but you can always try to prove people wrong. I have a small piece of coral outside, but it's crumbling, so it's going to be use for gardening purposes.
Surprised you didn't consider really nice decorative pieces of driftwood instead. You must see a lot of really nice pieces when you're out in the water/forest.
Coral comes in black?
Divider is plexiglass that you had cut & drilled?