Rat Snakes can and do hunt hummingbirds. They sense (taste) the birds around feeders and will use the sit-and-wait strategy. Successful attempts have been documented. Wayne Irvin sent me an"after" photo a number of years ago. It was not a good shot -- but one that he was just barely able to get after running for the camera.
I have had (a) Rat Snake here moving in the Holly Tree toward a feeder on more than one occasion in the last couple summers. I am confident it was honing in on the birds since I have had zero other food-sized critters on or around the sugar water.
Note that also Chinese Mantids, Bullfrogs, and Green Herons, among others, have been seen taking hummingbirds in the eastern US.