From experience of dumping obscene amounts of fuel on military ops, if you fly into your mates dumped fuel as he passes overhead a couple of thousand feet above it doesn't half stink up the cabin. We couldn't see any noticeable change in TGT and the engines didn't fluctuate noticeably but the windows got a little greasy.
Decided to avoid the trail after the first couple of days just in case.
I can also add that dumping whilst on the ground makes a mess too! Sorry Malmö circa 1992
