you are right, the resolution on the Z axis will be lower with a trapezoidal rod. However, you actually don’t need that much resolution, so for printing it’s still ok.
The motors used in the K8200 have 200 steps per revolution. Since the drivers (A4988) are set to their maximum in terms of microstepping, x16, the firmware actually needs to send 3200 steps to the driver for one full turn of the motor. In case of the Z axis, both values are of interest for calculating the resolution: theoretically, each (micro)step will move the axis by 1/2560th of a mm, or ca. 0.4 micron, with the default M8 rod. However, due to a firmware setting it’s best to calculate the minimum layer height increment from the fullsteps resolution, which is 6.25 micron.
Usual trapezoidal rods have 1.5 mm pitch (TR8) or 2, 3, or 4 mm (TR10 and above). For these rods, the min layer height is between 7.5 and 20 micron. If you want to print at lower heights, you should indeed select a matching rod with very low pitch, apart from other mechanical changes that may be indicated in such a case. Otherwise, you’ll be fine with any of the standard pitch TR rods.