I think people actually live back in there so I'm not sure if the road gets plowed or not. It's a gravel road all the way back to the stream once you get off Highway 17, and I think its posted as a primative road, which suggests to me that it could definately get snowed in at times during the year. You probably want check the weather in Soap Lake before you head over there in the winter, that should give a good indication of whats going on weather wise at RF.
My parents only live a few miles from Rocky Ford so I fish it a lot when I head over the hump to visit, especially in the winter. The fishing pressure decreases dramatically and the fishing is usually quite productive. In the 20+ years I have fished the Ford the road has never been impassable. The workers at Trout Lodge run up and down the road every day which helps keeps the road drivable. Also the area doesn't really receive as much snowfall as one might believe.If you can make it over the pass you will be able to get there. In fact the biggest problem will be keeping the eyes of your flyrod from icing up while you fish.