Yes.
It doesn't even have to be raining...if there is thunder and lightning, they will cancel.
This happened to us last May (and we had bought the H&V package). However, they did wait until the very last minute to cancel, so they were really trying to avoid cancelling. There was no rain, but ALOT of thunder. About twenty minutes after they announced that it was cancelled, the bottom fell out of the sky, so they made a good call.