I don't know if I buy the "oily bone" theory. First, if you don't have a deer bone, you have to brush cordovan until your arm falls off, the idea being to bring the oils already in the cordovan to the surface. I have also polished out scuffs in cordovan with the back of a tea spoon. And no, it wasn't a greasy spoon. I suspect that a deer bone does what a brush does but more efficiently.
Certainly, when you use a bone on waxed calf, any oil in the bone itself is pretty irrelevant.
On a side note, I prefer cordovan with the mellow glow that only cordovan can get rather than a high polish. This probably has a lot to do with my arm getting tired.