If he can sleep in a hammock, I don't see why he couldn't use one. Can also be used with a tarp and made bug-proof, so why not?
The temperatures, I travelled from Costa Rica till Mexico while I lived in Honduras for a year, the temperatures never get very cold, though high up in the mountains I would say a sleeping bag which brings you comfortably through 0°C would be in order. It shouldn't get under 0°C, so you don't need a heavy winter bag or something. You always could take a summer sleeping bag, and take for a the mountains a silk inlet with you, and maybe wear some extra cloths.
For real current temperatures, check google ;)