Yes....scouting by boat is an almost must. I used to hunt the Northern end of Rayburn....out of Marion's ferry (sp?). As with any lake, the water level will play a key role in your success. If the lake has been low all summer and comes up now or right before season......it shouldn't take much. East of M. Ferry and North of M. Ferry should show signs of ducks.....
Keep in mind that this area does not hold ducks like it used to. Granted, you will get good waves of ducks at times, but you will get frustrated. Be patient and you'll learn alot. I usually killed good #'s of teal and divers, with 1-2 mallards mixed in occasionally.
Get you a good topo-map of the lake and all of it's creeks/channels....as you can step off in a channel off a flat and get wet in a hurry!! Find you an area and learn it well. Once you've got that area down, try another area.
If you go WAY up the lake to where the river runs in......you'll probably want a GPS. When the water is up you can really get lost up there......really quick.
Watch out for all the damn canvasbacks.....they're offlimits until Dec.
Other than that, scout, scout, and scout. Get out there early and be mindful of other hunters. Don't set up too close to other hunters. Don't skybust. Just use your head and HAVE FUN!!!!
"Screw you we're from Texas.....we're from Texas, screw you." Ray Wylie Hubbard