As someone who has seen it from all angles, as a showman, fitter, producer, and judge, I think you have to look at your surroundings...growing up in Louisiana where a lot of Brahman's and Brahman influenced cattle are shown, you often see showmen in those breeds with hats on, however in the British and Continental Breeds and Clubbies you dont see many with hats.
I think hats are a matter of choice as long as they are clean, in good shape, and worn correctly, however if you are showing in one of the breeds or shows where people dont ussually wear hats, then you have to remember that the hat is probably going to draw a lot of attention...so you must make sure you want a lot of attention on the calf your leading...if you calf is good but has a few minor faults I wouldnt wear the hat because the hat is going to draw the judges eye to you more making it more likely he/she might notice small blemishes.
I personally have never worn a hat in the show ring except when judging and not always even then, but at the same time I dont penalize showmen for wearing hats either!