I agree with Maxx,
First off, I'm not much on "who could beat up who" type threads. If you spend anytime on a Star Wars message board, you can find threads about "Yoda vs. Darth Maul". Those folks get heated and those are fictional characters! If I were at a Gathering, and BJ Penn or Mat Hughes showed up, I would try to get through the line of people that would form. The Brothers would not form the line to see if they could "kick Matt Hughes a$$". The line would form because any member of the tribe would be crazy to pass up the opportunity to fight either one of those men. What a great way to see where you are at. As I moved into the line, I would quietly put a training blade on my person for use when (not if) either of those men would decide to close on me and start grappling. That would not guarantee a kill on my part, but maybe I could pull my knife, change their focus, and maybe even come away with a kill. Notice that I wrote "a kill", and not "a win". I would do the best that I could and after the fight, I would try to get the perspective of Penn or Hughes on DBMA. What do they like about what we do? What do they see as potential holes?
I'm also not big on trying to one-up someone on a thread with a hypothetical. What if aliens land who use telepathy as a weapon? Does that make all of what I learned about myself through martial art invalid? What if they can stop bullets and knives can't penetrate their skin? What if you can't eye jab, scratch, or bite the aliens? All that means is that you're talking about a situation where your martial art is not an appropriate solution. Do you eye jab, double leg, and then take a section out of the cheek of a drunk uncle at a party who wants to test your kung-fu? Do you tell a 350 pound mugger to change leads?
I think that everyone out there needs to remember a key idea of the original UFC: what happens when there are as close to no rules as possible? No longer can you fall back on, "I'm a killer. If I unleash my full power, people will die." That was the arena in which to prove it. That's a theme that has been maintained through the Gatherings. It's as close as one can come to reality. No longer can you say, "I'd just drop them with an angle 1." Prove it.
If I spend enough time on the Web, I can find negative threads about almost anything. Now on the thread in question, it seems like there is the suggestion that because DBMA doesn't really bite, scratch, and eye gouge, it's not real. Nobody who has fought in a Gathering doubts the validity of DBMA research. That's good enough for me.