Those drip rings keep the hydroton pretty uniformly moist- Waterfarms work surprisingly well.
You might have to hand-water the cube w/ a Tbs or so of water for the first couple days, but it'll root in fairly quick.

If yer worried, fire it up w/ just a RW cube ( no seed/cut) in the center for a couple of days ( take the plastic off the cube, if wrapped) and watch what happens.