You looking at the GARF Aragocrete? I'm pretty sure those guys know what they are doing.
You can place any plain rock into your system and allow it to become 'LIVE'. It just needs ample space for critters to hide and needs to be seeded correctly. I think it's great not using anything directly from the ocean. I'm going to purchase a whole bunch of aragocrete arches and caves for my mothers tank at the end of July and just seed it with all it needs.