You should address this question as an immigration matter, as it deals with deportation more than it does with the DUI. The fact that he is here illegally is why they are most likely wanting to deport him and not because he got a DUI.
It sounds like you are asking about the immigration consequences and not the criminal consequences for DUI, so please repost your question to the immigration law section.
The fact there is an immigration hold on him preventing him from being bailed out on the DUI charge is concerning, as is his illegal status. Since he is here illegally, he is going to need a good immigration attorney and/or a miracle.