As for drone pics, as long as it's being operated in compliance with FAA rules [www.faa.gov] it's legal. Whether it's appropriate under the circumstances is a judgement call. At least for now, I don't think railroad yards are usually considered restricted airspace by themselves, though if in higher than G airspace otherwise (near a larger airport, for example) they might be incidentally.

There are court cases going on regarding violation of privacy by use of camera-carrying drones. Results so far are inconclusive and only at the trial court level (including the guy in KY who shot one down). I don't think tank cars have an inherent right to privacy, though if a corporation is a person for political contribution purposes perhaps NWP can claim a right to privacy on its property (owned or controlled).