The timber hitch holds fine on a pole without bark as well. It needs a fairly large cylinder though and it does not react well to changing loads and vibration. It tends to work lose under those conditions.
I was in an emergency respond team and we were not allowed to use the timber hitch for securing people or for really heavy loads. So strength did not really matter. The main use was for transporting smaller timber (a size one or two people could lift) vertically. It was always used in combination with a half hitch on the other end of the timber.