Not really, some were modelled internally at Turn 10, while others were modelled by Dhruva interactive (an Indian company: http://www.dhruva.com/newsite/inside.html#%20Games%20Art%20Studio,Projects ).
As for weather effects and nigth racing, Turn 10 dropped them because they couldn't achieve a steady framerate with 16 cars. Obviously GT5 had them all from the start: 16 cars, steady framerate and night racing (and night time weather effects)...
Turn 10 using Dhruva Interactive didn't hurt the game any. I think that Pholyphony Digital should use their help also that way Gran Turismo 6 can come out before 2016.