Just touching (?) -- yes, you should be OK. But you are also on dangerous ground. There are two applicable rules of which to be aware. The first is that when entering the ruck your shoulders must be above or level with your hips. The second is that you must be supporting the bulk of your weight with your feet. If you are leaning on the ground or another player, then you are deemed no longer on your feet and have a duty to roll away from the ball. Of course these types of calls are subjective, bu the fact remains that if your hand is for some reason touching the ground, then there is a good chance that the official will judge that your are violating one of these rules and penalize you. Bottom line -- it is a generally good idea to keep your hands up and off the ground if at all possible. It also keeps opposition players from "accidentally" stepping on them.
Do as BLM said and you wont go wrong. On the other hand, what the ref can't see he can't penalise. Old school breakaway.
