For QS9000 you may well need to do an MSA (R&R). But certainly these do need to be calibrated. You will see out-of-tolerance readings. If they are mounted on surface plates, even a small amount of contamination built up on the surface plate may be enough to cause out-of-tolerance readings.
The A to D converters in the digital indicators do have some amount of drift over time as well. And so there is the need to check and adjust as needed to assure accuracy.
Bottom line: Calibration is needed. R&R would be as necessitated by your product parameters (sounds like probably it is needed).