The way I see it is that if Jeep aka Daimler Chrysler can claim that the Liberty made it through the Rubicon by takeing the Bypasses and stacking more rocks than the law should allow, then the X should make the rubicon also. I would expect damage though.
Now about breaking an axle on the trail. It could be repaired on the trail with an X. But, who carries them. I've never heard of "any" Nissan H233B axles breaking on the trail. In my opinion, it's safe to say that the Stock Nissan V6 engine is way to anemic to break a rear axle. But Fluke's do happen from time to time.
Rule of thumb for spare parts.....
If you have broken it before, carry a spare.
If you have seen someone else break it before, carry a spare.
If it looks like it might break, carry a spare.
And don't forget the tools to install your spares.
Cliff