Not in the fridge, no. Mealworms are dormant in the fridge.
I breed and feed lots of mealworms to my lizards (1 or 2 meals per week, depending on the lizard and how often it eats, are mealworms for my lizards).
You can gutload them with any dry foodstuff you would offer roaches or crickets- mealworms will live on and breed in such foodstuff as a bedding.
You can also offer a bit of fresh fruit and/or vegetables along with the dry stuff. Again, they will eat about anything you would offer more popular insects like crickets or roaches. If you are gutloading, you can offer more, but if you are maintaining a breeding colony of worms, you will have to offer a bit less- only as much as will dissappear in 24-48 hours, a couple of times a week. If there is constant moisture from vegetables or fruits, you will end up with dust mites eventually in your culture. So you want to allow things to dry out for at least a couple of days between feedings.
The wheat bran, cornmeal, and oatmeal that are popular with mealworm breeders are far from the most nutritional stuff that can be used to raise them in, and can be omitted altogether from mealworm fare or used only as a small part of a wider variety of dry foodstuffs. Use roach or cricket diets instead.