I think I would contact guest services on that question. I would not risk relying on information obtained outside of the company. Would not want to return the next morning and find your vehicle gone.
This is the correct answer above. Call and inquire. The rules change. I believe that you are NOT permitted to leave a car overnight at any of the park lots, nor at the Disney Transportation Center. Call and ask.
According to a friend who is a Security CM, cars left overnight in the theme park lots will be towed away by morning. (I asked her this last year, but I can't remember why)
On one Disney Board, maybe this one, I do remember reading someone complaining that their car had been towed from a theme park lot after they'd met some people in a park and went back to their Disney hotel to party.
They just assumed they could catch a bus to the park the next day and drive off.
But alas, no car was waiting the next morning.