First, I don't keep, nor have I ever kept, cichlids -- so if someone with more experience weighs in, I'm happy to learn as well.
That said, limestone will raise the pH of your tank. Whether or not you'd want to use it would depend on what your pH is naturally without it -- if your tank already has a relatively high pH, you might not want to raise it any more. Also, were I to add it, I'd do so slowly, so as not to raise the pH too fast and thereby stress the fish.
Good luck!