What is the law regarding per diem rates for travel and independent contractor/employee status?

There are two different issues here:

First, the law does *not* require ANY per diem--companies may make employees or contractors travel and not provide them any reimbursement, per diem for expenses, etc. (though a contractor will typically negotiate expenses into the agreement, or else not take the job). If you are not reimbursed, you may be able to take some tax advantage of the costs--this can get tricky, so discuss it with a tax preparer--but again, they don't have to provide you with any per diem.

Second, whether someone is an employee or an independent contractor has *nothing* to do with what you are called or how the company wants to pay you--it is based only on the nature of  your duties and the control exerted over you. Typically, set hours, use of company equipment, and the necessity to report back daily are indicia of being an employee, not an independent contractor; if you are in fact an employee, you may be owed benefits, the employer's share of FICA, overtime when applicable, etc. From what you write, it may be worthwhile to consult with an employment attorney to evaluate the situation in more detail.