Go for it! If your worried about it getting too soaked, just dont bury it so deep that just the bottom 1/3 is getting hit with water. but make sure u have something covering the top of the rockwool to prevent algae.
Rockwool is a great media. It will usually hold the perfect amount of moisture throughout if you use the technique I just described. I use 4 inchers to start mine. But i have 5 gallon pots on my ebb and grow and I bury them pretty deep as they are already vegged and ready to roll.