In a traditional kaitenage, the arm is thrown across the back and the nage moves like a discus thrower. This complicates the ukemi, since it adds a torque to the throw. Trying to do a normal forward roll becomes difficult.
What I've been taught and do, is jump. As soon as you feel the throw coming on, you jump into your forward roll. You can't wait for the nage to complete the technique or else you'll go spinning off at an angle and land on your side.