I think an adult passenger of a DUI accident has a right to sue in Canada, since the driver was initially suspended for a previous DUI. The passenger should consider consulting with the driving laws and regulations within your State to make sure that he or she has a case against this driver. Visit an attorney for more professional advice.
Why did they get into the car knowing that the driver was under the influence? They had a choice. The car that got hit did not. If I was the judge or on the jury I would say no. But any medical claims should be covered by the drivers insurance.