Was he convicted of the DUI? And did this happen in WI? If so, I'm sure Attys here on AVVO from WI can speak to first time OWIs in WI and whether they are crimes. If your son had an atty you may want to ask them as well. If you are still unsure after your exhaustive search, honesty is always best policy. Good luck.
Unless the record of conviction is sealed or expunged the only truthful answer is "yes". While Wisconsin lawyers should ring in on this, my preliminary research pulls up a request for expungement of a conviction, where the applicant is under 25. See the links below from the Wisconsin State Court System.
Every case and situation is different and vary greatly depending on specific facts. My posts are not to be considered complete answers to each question. My posts do not constitute an attorney/client relationship. I am only licensed to practice in the State of Florida and in federal courts. Florida Bar #337821, admitted 1982.
It is a legal question.
Review the advice posted by my colleagues who are admitted in WI, as there answers will be the most informed. I would also advise you to speak to the lawyer who represented your son. He or she can tell you what level of offense he ultimately led guilty to. Once you have the correct information, my advice is always to be honest on any application. Better that disclosure of these facts comes from you and is not discovered later.
Two things to consider:
1) if this was a first offense occurring in the state of Wisconsin, your son has not been convicted of a crime for this OWI. First offenses are only a civil forfeiture actions similar to a speeding ticket.
2) it is of questionable legality for an employer to inquire into your son's arrest and conviction records. These questions must be tailored carefully and and answered in specific ways to avoid revealing information the employer is not allowed to know. First, arrests are out of the question, only convictions are okay to ask about. Second, unless the conviction relates to a specific job duty or qualification, how many or what type of convictions are also out. (eg child sex assaults can be asked about to work at a daycare; DUIs can be asked about to be a cab driver but other things are not allowed).
If your son got his OWI/DUI in WI he can comfortably answer this question No (unless of course he has other criminal convictions).
However, I would also state, that some of my out of state colleagues have mentioned expungement. This would not be available in WI for any OWI conviction as it is specifically excluded from the expungement statute.