if you have a sump (the best filter for a marine tank or tropical for that matter, in my oppinion) then why would you want to put live rock in it? you would be better having a pre-filter a skimmer a biological bed (just a section of coral gravel) and then a couple of return pumps. you can then put the live rock in the display tank. you want to aim at turning the tank volume over through the sump 10-15 times an hour. this will cut down the time that toxins reside in the main display tank. I would also put a phosphate remover in the sump to.
you can put algae in the sump but for this you will need a product called miracle mud that dosn't come cheap. if you are just starting aut in marine fish keeping, then i would stick top the tried and tested methods.