Gorgeous horse, Spyder, and lovely photos of him competing in both disciplines.
There's no doubt that a talented horse with the right conformaton, attitude and training can be successful in both disciplines. The original title of the thread, and subsquent posts by the OP, weren't really addressing the horse, but the rider.
And my take, and my continued posting in this thread, is that the OP thinks that a hunter rider is just an undereducated dressage rider, or a rider that hasn't had their eyes opened. This opinion is further solidified by the OP's statement
...already having that aware, centrally balanced dressage seat would give them an advantage in the hunter ring
No, it's not an advantage. It's a lack of understanding of the fundamental goals of the discipline. And it's incorrect. A hunter rider is not a dressage rider that hasn't learned to sit up straight yet. Hunter riders ride "forward" for a reason. Different discipline, different goals, both valid *but* different. Cross discipline education is wonderful, and can always give you new tools and perspectives to apply to your primary discipline *IF* you approach the new discipline with an open mind. I do not suspect the OP of this.
Finally, if I rode down the center line of my test in two point or with my body inclined ahead of the vertical; and rode the rest of my test on a hunter style contact I would expect to be marked down on position and submission in the collective marks.
If I rode into the hunter ring in the OP's "centrally balanced dressage seat" I would not be competing on a level playing field with the other, conventionally forward seat ridden, hunters. Even if I was on a beautifully moving horse, I would not expect to pin as high as the horses that could maintain consistent gait *WITHOUT* active contact and seat aids. And in a hunter seat eq class, even if I managed to nail 8 spots and two changes from a consistent pace from that seat, I would expect to pin lower than the forward seat riders....because the name of the class is "Hunter Seat Equitation." Not "highly evolved equitation for riders who have realized that dressage is the one true grail."
Spyder, I hope you realize that the sarcasm is not directed at you, because I hope you know that I respect you and value your opinion. I know you to be a true horseperson with a *great* cross functional perspective. I also hope that your remember from previous threads that I have great respect for the principles of classical riding.
This thread has rubbed me the wrong way from the first post, and for the people who are willing and capable of hearing it, I have made my point several times over.
Please feel free to continue with the discipline chauvinism; I'll try to restrain myself from posting and spoiling the fun going forward. (Forward? Get it? It's a pun.)