I think the biggest problem with a wet night race would be the glare of the light reflecting off of the water – however, in Pirelli’s wet tyre test at Abu Dhabi, at night and with water sprayed onto the track by a special truck, this didn’t seem to be a problem:
http://1.bp.blogspot.com/_Yjpc_eruYBo/TTXWPGbuhUI/AAAAAAAAJow/PtxGwGiTFVg/s1600/pirelli_tyre_test_abu_dhabi_2011-7.jpg
The only problem with a wet Singapore race, then, would be whether they could finish the race – Singapore is very close to the two hour limit as it is, and with slower Pirelli’s this year I doubt they’ll do the full race distance on dries, let alone in the wet. But whatever happens, the race will go on!