Greased!
Unless you're talking about the ramps on a slipper clutch, grease should be nowhere near it.
As for cleaning, you'll find that the plates themselves will be cleaner in an open cover than a standard one as the dust created by the friction material goes elsewhere...like all over your right boot
Water just falls out of the bottom of the casing- it's all sealed up behind the clutch so nothing to worry about there.