Can you smooth a stepper motor with diodes?
I think @JMS may be on to something there, where the dead-band might kick in when the drive voltage is close to the back-emf from the stepper coil that circuit would introduce a large impedance in the line letting the motor free-wheel.

I have never seen this done, and it would really depend on how the controller works and what the motor is supposed to be doing. From the link you posted it appears the driver is sending a linear drive signal so this answer may make sense. It might make it a bit less "twitchy", reactionary, I suppose, relying on the inertia of the mechanism, and the motor likely "sounds" different.

If so the "print" would indeed look different, but again, depending on what you are printing and how much of it falls in that dead-zone, the results could be better or worse. I can imagine situations where, if you are dithering the head back and forward at just the right speed the dead-band could actually introduce a resonant oscillation.

As such, I think if I was going to add this to a printer I would also add a 4-pole switch so I could by-pass it and test print with and without it.