I also wonder if there's a bit of a Deathworld thing going on with the planet. In Harrison's book, all fauna was essentially telepathic, and was enraged against humans fighting back or clearing human space. However, I think that, in this case, there might be (a) larger consciousness(es) at work. I don't think the the thing that Folly met while ECA was human (ECA = Extra Corporeal Activity, like going EVA, but your body is the vehicle, and after this becomes a buzz word just remember where you heard if first (-: heh). I think it was a native intelligence, connected somehow to the Ether.
I'm not saying there's nothing to the Iron theory. Many animals go into a frenzy over blood and it may be the trace iron in human blood that makes these creatures go into theirs.
Any speculation at this point, unless guided by a WoJ, is unmitigated WAGgery. That disclaimer made, who's to say that iron doesn't play a part in connecting to the ether and that the enemy Intelligence isn't also dependent on iron and it's not its connection to the animals that causes them to go nuts when they sense iron.