The NutriBullet is not the best option for a frozen margarita as it would more so liquify the ice vs. shaving it. The Party Bullet however, has a specific blade designed for frozen drinks.
However, ice works just fine in the Bullet. I actually prefer frozen fruit so that I don't "waste" any space with just ice, but still get the cold effects of the frozen fruit.
If using ice, remember to still use a liquid.