With toe-out, the tire at the inside of the turn will be "turning" quite a bit more than the outside tire, and we (pretty much) all have zero-Ackermann steering. On things that go fast, and therefore don't have stuff like spooled differentials or rigid axles, toe-out (and Ackermann) is desirable as the inner tire is doing the work. With a rock crawler, as soon as the wheels go to lock, some amount of weight is going to transfer to the outside tire-- so that tire is now what determines the turning circle.
This is why when you go to full lock and give it throttle, the rig will "surge," as one tire is trying to go faster than the other, but as they're bound together, they cannot. I've found that a little bit of toe-in in the front is more beneficial than toe-out-- because we're generally traveling slower than a walking pace. As speed increases, so can toe-out, at least until the point that it hastens oversteer.