There isn't any slack, but because of the geometry of the damper/mounting it does very little in the "straight ahead" position.
If you were to turn the handlebars from lock-to-lock at a constant speed and plot the damper piston velocity it would be an upside down bell curve (or a U). At the straight ahead position the piston velocity would be zero (as it's changing directions). Being that the deisgn is a simple linear damper, the amount of damping it provides is dependant on piston speed.
In other words, like Honda and everyone else says, it does very little 5 degrees either side of straight ahead, and really only performs as you corner more. WER, Scotts, RTT, GPR, etc, are all made the way they are so that they can provide strong damping regardless of how you have the bars turned, because their function is not dependant on a changing geometry of the mounting point locations.
This doesn't make the Honda damper a bad unit, but I would argue that for stability in stright line rocks/roots/washes/etc a traditional style steering damper can be setup to vastly outperform it.