It depends. Is it fully cured? If it is not fully cured, you definitely want to cure it. If you don't, it will cause your ammonia to spike. It will cause the same thing as a cycle.
If it is fully cured, you can add it to the tank but be aware, there might be some creatures that you don't want in your tank such as mantis shrimp. They say before you add it to your tank, put it in a trashcan, mix up water to the salinity tune of 1.040 and let it soak for 1 minute. It will drive all creatures out of the rock and you can do away with whatever creatures you don't want. You can also take a red light and look at night and see what's crawling around.