In P1 we just got a really nice shot of the renault exhaust in the wet – it would appear that it does cause some evaporation on the track – each time it blows out a cylinder full you see a little puff of steam a little downstream of the exhaust exit.
But...
1) No where near enough to dry the track – calculations by people above prove accurate
2) Not in front of the rear wheels – out to their sides a little – I'm pretty surprised by how much they seem to be blowing the gas out the side of the car rather than under it.