Isn't the bedsheet heist just as plausible with a human behind the wheel? There's a chance he won't see the people in the road or will choose to run them over, but if he does the decent thing then he's a sitting duck.
Well you'd have an eyewitness that you would need to attack, who is potentially armed. I imagine the solution would be comparable to whatever security protocols ATMs have v. bank tellers.
You are overrating how far truck drivers would go to resist a robbery. That's not their job, and the load is insured - even if a driver is there, they're not going to do anything to stop you.