I think technically you do need rudder for a perfect roll.
Apply no elevator at the beggining, simply aileron.
Rudder is required before, at and after the perfect knife edge position (wings 90deg to horizon).
Then depending on the type of plane, your c.g location, engine thrust angle, etc, etc, you may need some down elevator at inverted.

Practicing slow rolls really improves your fast rolls. Leaning to use the rudder is very important, once you get confident with it, its not long and you are doing rolling circles and turns, loops,etc with rudder only. Then add elevator into the equation, and you have harrier rolls, 3d loops, etc.

Do things properly from the beggining and you will never stop learning.