You can catch fish out of Cumberland with the fly but it is more difficult than Dale Hollow just for the fact that there is more structure to fish in Dale than Cumberland. Dale has deep grass, shallow grass, black shale, chunk rock, better points, ledges and humps that all will hold fish at certain times so you get more of an opportunity to pattern the fish. Cumberland has deep clear water but except for the banks, pretty much a big bowl. I have never Seriously fished the fly at Cumberland but I know some fellas that have and it is pretty tough fishing. If I had to, I would get a good topo map and focus on the depth changes along the banks. Places where the contour goes from say bluffs to 60 degree or 60 to 30 degree areas of the banks would be the better holding places for the fish. Take into consideration the current elevation of the lake and it probably would be very helpful to actually draw the new bank outline on the map to better see these contour changes based on the current depth. I would say that later in the FNF season say February it would be easier to fish Cumberland because the fish will tend to be on the Bluff Walls more by then, especially after several days of unseasonably warm weather. You could fish the wall by Jamestown, Pig Pen, the wall towards Harmon and Difficulty, the wall on the left heading up into Beaver and Otter and such for long stretches to find the fish. I would think that Cumberland and Laurel would both be tough to fish the Fly on but they can be fished but I don't think with the success that one can achieve at Dale Hollow.