Depending on the source of the dead/dry rock, if the rocks used to be live and is being stored in a bucket/container, then expect dead stuffs to be released into the tank when you reintroduce them, dry rock (like BRS's kind) can also run the risk of phosphate leaks.
Alternatively, you can consider cycling them in a tub or bucket, seed it with another piece of live rock (or bacteria in a bottle, eg. Dr. Tim's). Personally if the tank is established, I wouldn't worry about dropping in some clean "dry" rock into the tank. Just try not to stir the sand bed too much.