Remember, weightlifting is cardiovascular exercise. The heart has to pump harder during lifting to get blood to the extremities and thus gets stronger. I don't think one necessarily needs any other form of exercise though of course other stuff may be beneficial for some goals and situations.
I am starting to do a small amount of sets with dumbbells to benefit my biceps, shoulders or whatever muscles I feel are neglected with snatches and cleans. I recall a football coach telling me that overall body strength was important for injury prevention even if particular muscles are not heavily used in a sport. With that in mind I don't think it's great that I have so little arm strength, for instance, that I have a tough time curling 50 pounds.