From your description of this situation, it sounds like you are correct in thinking your father-in-law has a substance use problem. It is not possible to know from the description how serious his condition is — either immediately or over the longer term. Since only about one in every 20 drunk or drugged driving incidents leads to an arrest, it is likely that his condition is serious and his arrest could be an important teaching moment if used properly.
I have one positive and one negative suggestion. Negative first: I do NOT think the man needs a "detox in Ohio." If he did, he no longer did by the time this message was received. Also, detoxification is only the beginning of treatment and not useful by itself. Based only on this brief description, your father-in-law needs long-term, continuing care - probably mandated as part of his eventual sentencing or added to the existing sentencing.
This is the basis for my positive comment. It may be difficult to talk with your father-in-law directly, so I suggest talking to his parole/probation officer if he has already been sentenced - or speaking directly to the judge if he has not yet been sentenced. Prior to that, I suggest identifying 1 - 3 good outpatient treatment programs near where he lives (which could be the specific recommendations used by these authorities.) I have found good reception by parole officers and judges under similar circumstances. It does not matter if he wants to go at this point; motivating him is part of the role of the parole officer and the treatment program. I expect a good outcome from this situation.