live rock is different to normal rock in the fact it is very poreous so you wouldnt be able to use normal rock unfortunatley. you can use base rock but again this is live rock that has dried out.
the reason you need the poreous rock though is because in the pores it can produce bacteria that break down ammonia to nitrate then nitrates into harmless nitrogen gas whereas normal rock and bio balls can only convert ammonia to nitrate. so lr will help keep parameters down in the tank.