how do you figure inverts can be an Ich carrier?
Ich's lifecycle needs a calcerous substance to bury itself and grow during the tomont (?) stage. this is why its important not to have sand or rock in a qt tank, and why it is unlikely but plausible that it could come in on a coral skeleton or rubble it is attached to. As far as i know it cannot do this on an invertebrate exoskeleton. however , it is possible that the next stage of the life cycle, the free swimming phase, could be in the water of an invert you are adding, but that is very unlikely, and almost impossible to be a threat if you follow normal convetions of never adding LFS or shipped water to your system.
as for QTing inverts i dont think it is necessary as they have very few diseases that are known, and cannot cross-infect fish with anything. also if the QT tank had ever had medication in it (IE copper), then it is especially a bad idea.