Two things...
First, he can still train with his instructor, but can't solo -- no medical needed to take dual.
Second, if you have a DWI within the past few years, the airlines won't hire you. This is due to an intersection between FAA rules and the air carrier pilots' contract. The second DWI within a certain time frame is by FAA rules a mandatory 1-year suspension of your medical. However, under the contract, alcohol-related issues are considered a medical problem. Thus, you are considered medically grounded while your medical is suspended, and you stay on the payroll while you "heal." That means the company pays you to sit home for a year -- not good for the bottom line. I've spoken to several major and regional airline hiring offices about this, and their position is clear -- while they can't fire folks who get a first DUI while working for them, they don't hire folks with recent DUI's because they aren't willing to risk the second offense. You won't find this in writing, but as long as there are folks with no DUI's available to hire, the application of anyone with a DUI goes to the bottom of the pile.