"but it is rare that someone gets hired when a DUI is on his record."

I don't think it's a show stopper. Especially at the lower levels of the ladder.

As far as DL being suspended, I'd tell him to go get a medical. If he comes back with one, I'd say go for it. I've never seen a reg that says it's the CFI's responsibility to find out if a guy has a drivers license. Maybe it's a new TSA thing, but I think he could prove citizenship and ID better with a passport.