For this recipe I would not attempt using cocoa powder. Cocoa nibs are comprised of about 50% cocoa fats, whereas cocoa powder is made by grinding the cocoa beans and pressing to remove all of the fats.  So using the powder (zero fat) wouldn't result in the same outcome. Plus, the aroma of the roasting cocoa nibs in your home is so satisfying and the extra step is really quite quick! I think you'll enjoy it. However, cocoa powder can be used to make chocolate. If you prefer to use it, I'd suggest finding a recipe that is designed for cocoa powder.