re: Question about defining an employee as a "independent contractor"

Based on what you presented he is definitely an employee and should be reimbursed for anything he paid out of pocket that should be covered by the employer (self-employment taxes, liability insurance, OT pay...), I do not know about the lost pay for health insurance and 401k match.

Did no see it mentioned, but federal law does require time and a half for any hours worked in a set work week over 40 hours (some states are higher). I'd imagine it's a safe assumption that he was not paid OT wages.

PTO, he would also need to look at the companies PTO policy to see if he is obligated to be paid for any PTO that he went unpaid (contractors do not get PTO).

He needs to go to the Department of Labor and discuss with them. He should also consider hiring an attorney; but as someone else mentioned he needs to look at his prior tax returns.