Not at all, though it does help with temperature regulation. That said, you can totally make it work with a heavy-bottomed dutch oven so long as you have a thermometer.  If you’re new to frying, you may not realize that adding dough to your hot oil will cause the temperature to dip. Make sure you keep your oil at a nice, steady 340F to prevent either soggy donuts (from too low temps) or burned ones with raw interiors (from too high temps).