Are these GND connected resistors on the Arduino Due redundant?
Yes, they are redundant. They are elements of resistor arrays (multiple resistors in one package) that aren't used. They have just connected all unused pins of those packages to ground.
If you want to know why they would have unused elements, it's all to do with optimizing the manufacturing process. If you have, say some 100k arrays elsewhere in your design and you want to have maybe one or two other 100k resistors elsewhere, rather than adding another component of a discrete 100k resistor it's cheaper to use a 100k array and not use some of the elements. One of the factors in the cost of pick-and-place operations is the number of different components. By keeping the number of component types to a minimum they keep the manufacture costs to a minimum.