Keith,
I thought that the "balance" ball was telling the truth in the OEI case: when wings level/ball central, it is telling you that the rudder force is balanced by the lateral forces generated by the sideslip and when flying straight, ie bank/ball into the live engine, the rudder force is unbalanced in the plane of the wings but is balanced in the horizontal plane by the lateral component of the slightly banked lift (TR) vector.
Stay alive