I've got a "Deluxe" version of the late 60's Falcon 56 under construction. It will not have ailerons. I built one 38 years ago and solo'ed on the third flight, also without ailerons. On that one it was powered by an OS .19 and controlled by an Orbit 4 channel radio with 3 PS-4 servos.

As to dihedral, there is no fixed rule here. Low wing airplanes typically need some to be neutral to rudder (the plane will yaw, but not turn). The same amount in a high winged airplane will allow the rudder to steer it.

As far as a flat wing not being controlled by rudder, it depends on the design. I did all the directional steering in the glide of my Stingers (a Formula One pylon racer) with rudder only, as the ailerons did almost nothing when slowed to less than 40 mph.

A good Class II design from the early 60's will do almost any manouver that an aileron model can do, with the exception of knife edge flight. If you ever get the chance to fly a Stark Shark it will shock you what rudder and elevator can do.