:yeahthat: dental can be a possibility here for sure. If it hasn't absolutely been ruled out, I would bring it up to his vet again.
HOWEVER- some rabbits after a bout of GI stasis are picky for a little while over food. One of my guys had constant GI slowdown all summer, and he would only eat a couple of his favorite foods and leave the rest. Their gut takes a little while to recover. If he has/had hair in his tummy he could still be feeling full from that, and only selecting the food he likes best. Your rabbit is trying to eat his bedding because he is craving fiber.
What you want to do is get as much of that hair out as possible and hydrating him will do that. I would keep giving him all the critical care he wants to eat for now (really wet it down), and all the romaine he can eat (if he has had large amounts of it before). It is likely that as he passes more hair in his poops, he will begin to feel better and eat more of his normal diet. Adding the fresh pineapple juice (just a wee bit) to syringe feed to him may help break up the mucous holding together that hair.
Sometimes it takes a while for them to recover from a GI episode, believe me on that one lol. My guy took months to recover
:time: and he still has acute 'episodes' no one can explain still, but is otherwise very healthy. Keep doing what you are doing because I think as long as he is hydrated he will continue to improve.