It does, indeed, evapourate-sooner or later.
I was once dumped upon by a SAR heli on it's way to a close in emergency. The machine passed almost directly overhead at about 500 feet agl with avtur pouring out of a dump valve. All that reached the ground was a strong smell of kerosene.
However, that was on a good day.
A friend tells the story of an extreme low level dump on a four engined piston following engine failure on take off from a bush airfield . When they read the evening paper the headline was "Mysterious fire destroys village huts near airport."
Another friend of mine was observing an RB47 taking fuel from a tanker when the hose broke. Almost neat kerosene went into an air intake and...boom..the whole aircraft blew up.
I seem to remember that a 707 was once lost during a reported dumping session that entailed flying near a Cu Nim.
And of course the old apocryphal story of the USA based 707 taking off from LHR who advised air traffic that he had lost an engine and was dumping immediately, heading towards Windsor. Air Traffic immediately responded informing him that he could not dump on that track and the captain's reply was reported as:
"Better call the lady, collect, and tell her that she either gets the fuel-or the entire g*******d airplane!"
I certainly always followed the advice to never dump in a holding pattern, particularly when descending, in case I flew into my own kerosene vapour trail.
Fuel dumping is a serious event and it may be safer to land heavy.