Is cardio needed for contest prep and fat loss? As a general rule, yes - but not always.
During contest prep, the basic rule behind losing body fat while retaining muscle is to maintain protein intake. You need to eat at least one gram of protein per pound of lean bodyweight and minimize calories using fat and carb manipulation.
During this time of calorie restriction, you will trick your body into continuing to lose fat by scheduling low carb days mixed with moderate carb days, with one high carb day added in. That high carb day will be your "binge day" or "cheat meal".
Personally, I would typically do one to two low carbs days immediately after my high carb day, followed by a moderate carb day, a low carb day, and back to moderate.
It is key to keep things mixed up each week and plan by both feel and progress. At some point even this manipulation will becomes less effective for losing body fat. Now it is time to add cardio to your contest prep. I would add 2 to 3 thirty minute sessions at 80 percent of your max heart rate. This is a fast walk, not a run. By adding this cardio routine to low carb days you will make them calorie deficient.
But be careful not to burn too many calories, where you would be burning muscle as energy (catabolic) or burning the protein calories that you consumed to fuel the cardio. Remember, your goal it to burn fat and hold onto muscle.
A qualified, experienced personal trainer who is knowledgeable about contest prep can help you determine how best to introduce cardio, so you can retain the muscle you need and lean out so that you can be considered contest ready on stage. This can be done either face-to-face or with an online assessment.