In the first tournament I entered, grabbing clothes would get you disqualified after a warning from the ref.
In the tournament I was in yesterday, one of the guys who reffed my match actually ALLOWED the other guy to grab my rash guard. I think that was just bad reffing.
I also saw a match where one guy was ahead on points, so he held onto his opponents shorts. He kept getting points deducted for that, and then he lost.
Personally, I think they should penalize anyone who grabs clothes in no-gi.