Presumably some nasty orientations are possible with normal knots, just maybe rather less likely (though I guess a normal knot might have the possibility of a true crosswise loading if the rope slips round the crab in a way that a clove hitch might not be able to do).
I suppose a lot comes down to just how much flexibility there is in the system.
I'm reminded of the old 'Oh my god, you can't hang a Stop on a 10mm long maillon - look, it's so easy to get accidental opening!' comment from someone demonstrating by manipulating Stop and maillon in their hands, with complete control over position, twist, torque, etc, whereas trying to do the same thing even just with the maillon attached to their harness is rather harder, let alone by duplicating the kinds of forces that a rope and/or cave wall might conceivably place on a Stop, due to the freedoms of movement in the system and the limitation of extent of manipulation that introduces.
If someone *was* going to use clove hitches, how much difference would the tautness of the lines make to the risk of misoriented crabs?
My first guess would be that even if people were moving along the lines in a pessimal way, there'd be some threshold of slackness below which misorientation would be much less likely to happen.