Is NASCAR so hard-up for drivers that they have to go to F-1/Indy for new blood?

No, quite frankly its the other way around. NASCAR is not hard up, open wheel racers are. Open wheel racers are beginning to realize that NASCAR drivers are regarded as the best drivers in the world, that because of popularity NASCAR is the place to be for recognition and money, and because NASCAR is so popular putting people in the seats is not an issue and there is some job securtiy unlike open wheel where attendance is way, way down.