I am unsure of the real reason behind the post. It is against all state laws to operate a motor vehicle while under the influence of drugs/alcohol. You. like every other citizen, can call the police if he is driving impaired. They may or may not respond and pull him over.
I am trying to give you a general answer to your question. We do not have an attorney-client relationship by this response on the avvo website. I have not been retained to represent you. I am licensed to practice law in Kentucky and in federal court in this state and the Southern District of Indiana. You need to seek legal advice from an attorney licensed to practice in your area..
I agree with Attorney Mascagni. If he drinks and drives he is stoppable-by the police. If you are concerned and witness him getting behind the wheel then alert law enforcement.
If your company has a policy concerning drinking on the job you can bring that information to management. Additionally, you can confront him and let him know of your concerns. If he just pled guilty, he probably has a probation officer monitoring his case. Drinking and driving would be a violation which would result in him being incarcerated. If all else fails, if you see him drinking and driving, call the police.