Free nights depend on the airline, some will provide a hotel room with a transit over a certain number of hours, others specifically state that they won't no matter how long the connection. F and J tickets with the higher profit margin are obviously more likely to obtain a room.
Booking a stop over can be a good option, giving an addition to a holiday and a break in a long journey. Emirates market Dubai as a stop over point and offer some good packages, the other UAE airline are trying the same with Abu Dhabi and offer some amazingly low hotel rates and are only a two hour coach ride from DXB.
China Southern may give a free stop over in Guangzhou