Bleached as in was dipped in bleach, or bleached as in whitened? Depending on where it came from, you should be okay adding it to the tank. The bacteria from your existing rock will quickly colonize any new porous rock, and the exterior will get coated with algaes and such as well.
If you suspect it was bleached, I would rinse it very well, just in case. It shouldn't still contain any chlorine, but being safe is better than being sorry.