For me, the B&H and teaching the dog the correct motivation for performing the exercise is complex. You have to know your dog's drive package. You have to train your dog that he is actually holding and controlling the helper with his bark in the same way he does with his bite, which is not natural for a dog. The bite is not supposed to be a prey reinforcement. You want a balance of prey, fight/active aggression and defense, which requires the right dog and the correct foundation training. Having said that, it becomes very difficult to get a correctly motivated dog that is actually holding, controlling and fighting the helper with his bark because you need a dog with the right balance of drives and the exercise is done so much in training, it becomes difficult for the dog to see it other than a prey reinforcement exercise.
IMO, teaching your own dog to do a B&H at any time interferes with the goals I'm stating. Topographically, the behavior kind of looks similar to a strong dog that is actually holding and fighting the helper with his bark, but in the dog's head things can be night and day. For example, most people know what a counter is when it comes to a bite. The dog bites the sleeve and then counters forward, gripping deeper and stronger on the sleeve. But a dog can also counter with his bark in the B&H, and if you or the helper don't know that, the training is incorrect and you end up just teaching the dog a circus trick of barking to get to bite the sleeve. A counter in the bark results when the dog is holding/barking at the helper and the helper is able to tap into some defensive aggression through his presence (which only really good helpers have) and the dog counters with his bark as evidenced by the bark becoming more serious for a bark or two or a change in cadence, etc. When that happens, a good helper will reward the change in the bark with a bite. So the reward is not just for prey barking but for a display of fight and defensive aggression. The other issue is that most dogs quickly learn that they are not going to get hurt doing the B&H, so it quickly becomes very much a prey game.
In a nutshell, hope you have a dog with some aggression other than predatory/prey, such as social, defensive/reactive, active aggression, that you have a really good helper who can elicit those types of aggression, and don't train you own dog to bark for a prey object because that defeats the true purpose of the exercise. It is a luxury that most people don't have to have a really correct and balanced dog and an exceptional helper to correctly motivate the dog in this exercise.