Sort of...The food sold with them is a "gut load" if you will, compared to feeding them carrots. This would apply to Great Lake Horn worms, Mulberry Farms, and Coastal silkworms, their food has been established and productive, I have had positive results from all 3 vendors recipes.
peel them off by grabbing them in the back 1/4th of their body and start peeling towards the head. They don't get hurt easily and if they are getting fed of anyways it shouldn't be a problem.
Of course they can be "gutloaded" as with any type worm that only eats a certain thing. Liquify your gutload and inject it into the worm right before feeding with a syringe.
Also you can put them into a container the afternoon before feeding them off and they will eat certain veggies and leafy greens. I've fed them red peppers/green peppers, collar greens, dandelion greens, kale, lettuce, grated carrots , sliced celery and just about anything else you can get cut thin enough so it's easy for them to eat.
EDIT: Collard greens, thinly sliced carrots and peppers seemed to work the best. You wouldn't believe how much of those three a single medium sized worm can eat in a 12 hour period.