It depends on what level. Open shows - sure, go ahead. In any breed show you could/maybe/might get away with doing performance halter, not regular halter. He's not fitted, and a little small size-wise. You might want to try ponying him/long trotting him for several minutes a day, just to put on that muscle mass and add a high % fat:protein feed if you're serious about it. But if you're just showing halter for fun to get him experience in the show pen, I wouldn't worry about the placings and just focus on training.