I'm not privy to all the details, but I'm pretty sure Tesla can't sell a pre-production vehicle even to an employee for road use. They would have to get that vehicle certified which costs quite a bit of money (plus the liability costs). That's why a lot of manufacturers just crush the vehicles. So the vehicles sold to employees are going to be production examples.
It's a different case if Tesla sold it to employees to be put on display (not road use), but I'm pretty sure not many people will take up that offer and we will hear about it.
AFAIK, vehicles sold by large mfrs must pass FMVSS, NHTSA, EPA. They are allowed to be updated. The problem is supporting 300 cars that could (will) have some component changes.
The reason they are crushed is because it would be more expensive to support than crush when the number produced is small. Tesla Motors is already used to supporting lots of early revision components.