6th Circuit Court of Appeals decision, Ellison v. United States - "a motorist has no reasonable expectation of privacy in the information contained on his license plate under the Fourth Amendment", and "so long as the officer had a right to be in a position to observe the defendant’s license plate, any such observation and corresponding use of the information on the plate does not violate the Fourth Amendment." They also emphasized that there is no expectation of privacy for a license plate or VIN that is required to be displayed on the outside of the vehicle, and an electronic or physical retrieval of records associated with that license plate or VIN does not constitute a "search" under the 4th amendment. So there does not need to be any observed violation or other "trigger" before a check of the plate is conducted.
Having said the above, I'm NOT saying what the OP cited was ok - that was a clear violation of terms & conditions, and is grounds for discipline. What I'm saying is I don't need a reason to run random plates I see during the course of my shift, but you're still gonna have some explaining to do if all your "random" vehicle checks are height/weight proportionate females with blonde hair between 18 & 29 years old.