If it is a survey, it is not a loophole. It is a legitimate exemption. If they didn't attempt to sell you products, goods, or services it isn't a legitimate Telemarketer. I don't like them or it either, but that's the way it is.
... the DNC may have exemptions for legitimate surveys and charities, however, they must still obey the law once you tell them to add your number to their internal do not call list.