Is it a legal obligation to tell an employer that I am on house arrest wearing an ankle monitor?

You probably need a lawyer to guide you if you intend to answer with semantics about these questions. Each answer will depend on what is precisely asked. Every state treats DUI's differently and in some states its a criminal conviction, in others just a motor vehicle offense even though it can carry a jail term. If you are trying to get a job in any field that requires driving as part of the job duties, I would err on the side of disclosure if the question is ambiguous. If the company feels you hid something from them, you may be fired down the road if they feel you had a lack of candor in filling out their application. Good luck to you.