Okay, one more update for today
Right, so I figured, perhaps the iOS version is just failing when we try to load anything from the override folder at all.
So I took a TPC texture from the erf texture pack that's actually in the game. I extracted it to a tga and I put it in the override directory. Nada...
So the game won't even load textures from the override directory which it's otherwise happily loading from the texture pack.
Anyone more experienced at this ever seen that problem before?