I wonder what difference it makes who visits ? as long as we get videos of ASICs performing, and pictures of the assembling line, then that's all the proof we need.
Don't you think by then that will be a moot point? BFL will probably have videos already posted of the things running before anyone visits.
I am fairly certain that they will have to sign a NDA. It will be just their word of mouth. which is good enough for me..