It honestly hasn't been proven one way or the other but crushed coral would inhibit you keeping sand sifting/burrowing fish/inverts. Don't get a sand sifting star, it'll destroy the microfauna in your sand, clear the sandbed entirely out in a month or so, and then die. My 215-gallon wouldn't even have enough to support it long-term in my opinion.
It's all preference for which you run with. I would not recommend mixing it as nature has a way of sorting the mixture and you'll end up with the look of crushed coral, without any of the ability of the finer sand. I'd go one or the other.