Can you reheat or cook frozen foods using the sous vide technique?

Put simply, yes. When cooking raw, frozen ingredients, the cooking time should be extended by at least an hour to allow the ingredients to thaw and reach the desired temperature throughout.

For previously refrigerated, cooked foods, the cooking time should be extended by between 30 minutes and an hour.

Times will of course vary from ingredient to ingredient depending on the desired temperature and thickness of that ingredient.