Any porous, calcerous rock will, in time, serve the same purpose (biologically) as live rock. It may not have the same aesthetic pleasure as "live" rock, but aesthetics are in the eye of the beholder anyway.
I have spent a lot of time underwater, and believe me, dishwashers, cinder blocks, and anything else that serves as shelter is a haven for marinelife. Fish don't care if its a coral head or a car tire, as long as its a safe refuge for them to seek shelter in.
UNLEASHED-
If you want to create a truly natural environment, you will also need to add predators, chemistry fluctuations, and seasonal changes such as lunar cycles, storms, temperature changes, tides, etc, etc, etc. Considering this, is LIVE rock really that necessary in a FO system?
BTW- most public aquariums do not use live rock, and the AZA sees no need for them to do so.
Once again... live rock is beneficial, but a good wet/dry and skimmer will suffice.