While I understand you had one lucky experience at the car rental place, I disagree with the generalization made based upon it.
I don't believe non-traffic violations are ever really check most aren't even recorded. ...Basically if someone really wants to find out they will but it would cost too much money and they usually aren't concerned with the non-traffic violations.
Criminal records are "recorded". Some (many) employers do check employees' backgrounds, and they are very interested in things beyond speeding tickets. It is costly to do checks, but is much less costly than hiring people with a propensity to commit crimes on the job. Many employers realize that.