I think I read somewhere that its not the actual amount of credits that doesn't allow you, Its the fact that those cars have been placed on a trading ban list...
So when you try to send a car normally worth over 1 Mill, Whats stopping you is the server recognizing that car as being on the no trade list.
Not the server recognizing the cost of the car.
So I would assume the same cars that were unable to be gifted, are still that way. Good question though. Test it yourself.