Quote from pvdrift :even with s2 cars? No.. demo servers can only host demo cars, no matter what the licence status of the drivers in there is.
On a side note, there is a good reason for this. When you pit a car, in the pit stool, another person can take over that car after the pit work is done, providing that the taker and the takee agree to it (via the connection list).
Quote from [RCG]Boosted :demo users wouldnt be able to see them...unless they are unlocked, which they are of course not. Theoretically they WOULD be able to see the cars because the content is there, unlocked or not that wouldn't matter. But i repeat, THEORETICALLY!