Sorry for the rant. No drivers license for illegals
The thing is that they are ALREADY driving on the roads, and they do NOT carry insurance, so in case one of them runs over your grandma, your only recourse will be having them deported (if it ever happens) and have their car impounded, and your family will carry all the hospital/funeral home bills.
OTOH, if they have a valid drivers license they can get insurance, ergo, your grandma's bill are payed by them.
If the licenses are the same as all others, they can put in the DMV's database a note about the immigration status, when something happens and a cop or another authority checks the DL number, they arrest the driver and sends him/her back to whichever country he/she came from. How 'bout that?
Of course the DL # check would happen if there's physical harm to others or if the damage exceeds, let's say $1500...
One way or the other, as I said, they're ALREADY driving... Who do you want to pay for granny's hospital bills?