It depends how trusting your pony is. Is he comfortable with being blind?
I think he could learn to do barrels if you got him comfortable with it before trying anything drastic.. ya know, practice walking around one barrel and work up. What I would see as a problem here is that barrels are timed and if you were going really fast and your pony got spooked because he couldn't see something, it wouldn't turn out very nicely.. =\
It seems like you and your pony have a great bond. Try it out and see if he has fun with it, but remember not to push him! =]