I don't know the exact answer, but it sounds like everyone you have spoken to in a position of authority with the State of Michigan has said he needs a valid driver's license, which would make sense.
I imagine the state has not gone to the trouble of making disticintions between CC's for DUI's if you really wanted to push the envelope you might find a loophole, but he is probably best taking the appropriate steps to getting his regular license back, but that is just my two cents.
Perhaps you could contact a DUI defense attorney in your area and here is a list of some preliminary info from each state on DUI issues. http://www.legalmatch.com/law-librar...uspension.html
Hopefully everything gets resolved and your son will learn his lesson and never drive drunk again.