Yes, it is possible to use a regular cake mix in an easy bake oven. Preheat the easy bake oven. Lightly grease and flour the baking pan in the oven. Take 3 tablespoons of your chosen cake mix and mix with 1 tablespoon of milk. Put into the cake pan in the easy bake oven and allow to bake for 15 minutes.
No. Your cake mix will not be cooked well. You can cook it but the result is scary as you can see the part part of the food wet. It is because regular cake mix contains eggs and Easy Bake ovens are too weak to cook an egg.