The only way to get a visa without a hotel reservation is either through Emirates, which he doesn’t have enough time for, or if his in-laws sponsor a visit visa for him. That option would cost them around US$ 140 and quite some hassle to go to the immigration department, etc. So it’s probably better if he does book a hotel through Marhaba Services on arrival.
The basic package will cost him US$ 164.-- and includes 1 night in a 3 star hotel, 96-hour visa on arrival and free transportation between the airport and the hotel. Look here for details.