If you seed it with bacteria from another source, it will eventually becomes live rock.
It is said a general good rule is to have 2lbs of live rock per 1 gallon of water, but that's up for debate since some rocks are more porous than others.
I have done both live rock and dry rocks. Now I personally prefer to have dry rocks because it is easier to aquascape them to the exact way you like it and have them secure properly without having to worry things are dying off. There are trade offs though, the initial cycle will take much longer depending on how/what you seed the dry rocks with.
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.
Make sure to clean your dead rock. It is Always a good habit to cook it before using ANY rock. It will become live rock rather quickly. You do not need to "seed it", however, seeding will speed up the process.