That is an awesome chair! one of the best I've seen. You want his lil feet to be flat not turned or curled so yes I'd keep them splinted. And to me, I think I'd keep up with what your doing and gradually get him to the place where his feet are touching so he can use his feet to push up and down. which will be another form of therapy. Can you also do water therapy that can also help with getting his legs moving better. Of course these are just my opinions I am not a vet by any stretch of the imagination.
Lets see if we can get
@Isaac 0 here and see if he can advise.
Fuzzbert is absolutely adorable