He does need greens more than protein at his age. But honestly the only reason for critical care is for calories and vitamins. I think you're already providing what he needs now that you're giving vitamins. But then again he went many years without vitamins so the added boost might be good for him. It's really up to you. Since you can get him to eat you don't need it so much. If you decide to get some you could mix a little in his smoothie.
If he can fit in the hide it should be fine. He'll go in it if he needs to. One of mine hasn't used his in months. I wouldn't worry.