sure people clean live rocks.
i'm quite certain many do.
but the way to clean it is really contraversial.
personally, i jet the live rocks with tap water to get rid of the surface dirt.
then i immerse the rocks into a pail of tap water for 5 mins to get all the stupid bristle worms out.
then i put the rocks in. this method kills almost all the bad stuff but the good stuff too.
but don't worry cause usally the good stuff grows back...infact, i've used this method all i still get lots of cute tubeworms and star fishes attched on the rock into my tank.
the other method is to brush the rocks while they are immerse in a pail of salt water similar to that of your tank. success of this i wouldn't know.
hope this can help!