I don't see why not if he enjoys it. I have a registered Doc O'Lena/Peppy San Badger lines gelding, and we have had him do a few LD's (even though he'd probably rather be cutting cattle). He can do OK because he is long legged and lean, not a stout guy, but it does take some convincing to get him to travel at a trot for 3-6 hours! He's pretty smart and conserves his energy well and will go no faster than he feels he can maintain, but I do get the feeling he's always thinking "Why the heck are we trotting along when there's no danger?". He his a super safe bomber horse in the head, so we keep him in good enough shape to do a few LD's if one of our kids wants to ride the race - he's perfect for them because he doesn't care if he gets passed and doesn't get excited to lope off with the mass start pack. Only because he isn't super psyched about it do we keep him out of more races and/or longer races. He does it because he's good natured, but he doesn't love it. But if your horse loves it and tries hard, AND you feel safe, that is really what matters. He sounds like your best buddy, and that makes it so much more fun than anything!