Spoilers are assumed here right? Given the summary itself is a massive spoiler.
The most perplexing thing about that episode is how 2 guys with a pistol and shotgun, facing 5+ armed baddies with assault rifles and automatic shotguns aiming directly at them from maybe 20 feet away, were not instantly dead once the gunfire began. That's .. comically bad, like an A-Team episode.
BB is pretty good about not showing us bullshit. It might show us things out of order, or in contexts we can't properly frame, but it never shows us bullshit.
The only rational explanation is:
Meth Damon's crew was intentionally aiming not to hit them.
Once Gomey and Hank are out of ammo -- and how much ammo can they possibly carry on them -- they have to surrender. Compare with the crew who took out a rival meth lab a few episodes ago. They came loaded for war. Also, capturing a DEA agent is probably less bad in the big scheme of things than killing one. Even for evil drug involved white supremacists.
The crew knows these guys are important to Walt based on the phone call he had with them that brought them out there. What's the best way to have extreme leverage over Walt to get him to cook for you? Save his ass, and capture the people that are important to Walt.
It works for Walt to have Hank and Jesse disappear so he has time to move the money. Meth Damon's crew doesn't know about the money, they just had coordinates.
That "don't expect me back for a while" line to Marie sounded really ominous to me when I heard it, and now I know why -- Hank and Jesse are going to disappear as prisoners/hostages. (Gomey may be killed, since he's kind of the redshirt in this episode, unfortunately.) Hank's investigation was already so damn far off the books I don't think they'll be seriously missed for a long time.
The one thing BB does well is never doing what we'd expect, and the natural expectation is for Hank, Gomey, and Jesse to be killed here. It does assume a lot of smarts on the white supremacists' part, and it's not like these guys are known for their tender mercies -- but just wanting leverage over Walt and the giant meth cook payday should be enough to explain the paradox of a massive gunfight where nobody gets killed.
(I've never been willing to predict BB since it's so damn great at being unpredictable, but this one for some reason I feel weirdly confident about. It's the only unexpected amp-up-the-craziness outcome that makes sense.)
edit: I also reserve the right to be 100% completely wrong about all of this. Just a hunch, but one that feels truthy in my gut!