If he is connecting to a Delta flight and does not have to change terminals he should have no problem. Yes, he will have to pick up his bag there in DTW and re-check it, but the bags normally arrive quickly. From what I have experienced the customs lines are not normally long like at ATL or JFK.

Assuming he is connecting to a Delta flight it will be helpful if he has a Delta boarding pass which will expedite him connecting after he clears customs.

If I could pick any airport to have a short connection at it would be DTW based on my 10 years of flying NWA and Delta.