Yes lots of people on this site have.
Yes it's true. Businesses hold the BFL permit which allows them to bring firearms into the country. With a Prohibited Goods Permit you are then allowed to purchase. The only people to really get Phohib Goods Permits are really LE or Mil (and even then not just anyone whos an LEO or Mil). To my understanding they're for Military excersises and training and LE training (so if you're a police officer you can't get a permit however if you were the Police Chief or something and talked to the CFO and got a permit so that you could buy these guns for police training then yes).
EDIT: Sign up for JOC and talk to the JOC Admins to get AV'ed.
EDIT2: Just saw your intro post on JOC, you'll find Airsoft here is A LOT different than in Taiwan, just a heads up. If you want a decent M4 then $400 is a realistic budget but you'll need to purchase mags and accessories separately. Just a note: I bought my M4 for $450 and that was just the base gun itself, a battery, and a RDS, no mags, no nothing.