My company is one, and a simple FOIA to the INS will reveal everything to be above board. The "burden of proof" is borne through the process. The proof itself is on file. Again, these are non-IT positions.
I presuming you are being accurate and truthful so I merely ask for my own edification what positions you can not find Americans to work at what qualifications do you require that Americans do not have? Certainly it can not be Doctors, or Nurses. These positions require liscenses.