We have been told by the Dine Line CMs that if the restaurant closes because of bad weather, you will not be charged a no-show fee. But if the restaurant is open and you don't keep your reservation, then you will be charged. All you can do is call the restaurant or the Dine Line to confirm that the restaurant in question (in our case it was BBRBBQ) is open. We got rained out, the restaurant did close, and we were not charged a fee.
We did do a F! package at RBT on a rainy night. It had rained earlier and was misting on and off when we arrived. The patio was full and there were heaters set out for most tables. The restaurant was trying not to seat more parties on the patio, just in case, so we waited longer for an inside table (which was fine with us anyway). Now that there are more tables inside, maybe the wait won't be as long.