Fat is pretty vascular, not as much as muscle, but still there. As mentioned above there is some shunting with exercise, but that mostly is from the internal organs. As you warm up, there will be increased blood supply to the skin, which is lined by fat, so there really is not a tremendous amount of shunting from fat. Depending on how deep the fat is, it can be quite vascular. I have seen some tremendous size vessels supplying the fat stores of some big folks.