Why are they exempt from helmet rules? Are they not a USEF breed?
They are. Look up the Arabian section and then the Hunter Pleasure section for attire rules.
Helmets are required for Dressage and Over Fences classes only.
Showbizz is basically correct (though the helmet rule applies to all hunter classes, not just the over fences, which is why we still have to wear a helmet for the hack). But Hunter Pleasure =/= Hunter, so the helmet rule does not apply.
If you were to look at the Arab Working Hunter classes (both over fences and hack), all the riders should be wearing helmets (but I think those classes might only part of the Arabian Sport Horse Nationals).
You don’t have to wear a helmet in western or saddle seat classes either.
Interesting. Thanks for the education.
Maybe the breed exhibitors have harder skulls than the hunter/jumper exhibitors.
Many arabian people that cross over into the open world do wear helmets, but the traditionalists who stay in the main ring often do not. If they are showing in a USEF discipline that requires a helmet then they must. It is difficult to tell someone they have to wear a helmet in a non USEF discipline especially if they are showing next to western exhibitors and I think the organization is having some old school holdovers as well as being worried about losing members. I think it will come eventually though.
This has been debated ad nauseum on the forum. No, some disciplines/associations don’t require helmets. Some people think you should always wear a helmet while on a horse, others do not. Both sides have their arguments and will never agree. You’re beating a dead horse, and it’s starting to smell. Being snarky is just going to make the other side dig in their heels more.
You can do whatever makes you comfortable and is within the rules of your applicable facility or governing body. Other people can do as they see fit for themselves.
The theory is that walk/trot/canter in an arena has less risk than jumping things, so helmets aren’t as necessary.
Harder skulls is another reason; changing the rules for hunter pleasure would be darn near impossible, because the riders and trainers are so darn stubborn.
Certified helmets are required in all over fences classes and all hunt seat equitation classes, even those held on the flat. Riders competing in dressage classes as well as main ring classes are only required to wear helmets when actually warming up or competing in dressage classes.
The USEF helmet rules actually caused a ton of problems when they first came out for main ring shows. What if the rider is schooling their western horse in the dressage ring? What if the dressage rider is on their western horse later in the day? What about a class like show hack or sport horse under saddle which are sort of like dressage and hunters?
Oh, breed fanciers — Another question for the uneducated:
Why the white lab coats on the headers in a pleasure driving class?
Lab coats an easy way to look decent when you come into the ring.
I am the only dressage person at an Arab show barn. One other lady wears a helmet. All the rest, including the trainer, do not. I know a lot of dressage trainers who dont either.
Having had two conversion experiences myself I would never go back to my helmetless days - but I rode for many many years without. Still lots of people who do. To me they look mighty weird without but they think we look weird with.
Oh please, the greatest sin is seeing a gorgeous Equiline Shadbelly on a pretend dressage horse (show hack). 
