I would imagine only on the very high end of brackish. I once tested various types of macro algae by reducing the salinity over a few weeks but none of them survived when the SG was less than 1.017. All those little pods and sponges on live rock are really dependent on a marine environment.
One option is to get live rock and soak it in a mild bleach solution to kill of everything that would otherwise die anyway and pollute your water. CaribSea makes a product called Reef Bones that you might want to look at. The rocks would be 'live' in a way that they have a good surface area for your bacteria.