Yes, you can do cardio during SD. However, it is important to understand the pros and cons.
Pros
- Increased fat loss
- increased cardiovascular "fitness"
- Its really good for you
Cons
- The effect of endurance training on muscle tissue tends to reduce the hypertrophic effects of resistance training. The end result is a compromise between endurance and size.
- Endurance training will alter your power/speed
So make your choice based on what your goals are.