Notwithstanding any other provisions of this article to the contrary, any employer, workers’ compensation insurance carrier, self-insured employer, or group fund, may contract with physicians, hospitals, and any other health care provider for the provision of medical services to injured workers at any rates, fees, or levels of reimbursement which shall be mutually agreed upon between the physician, hospitals, and any other health care provider and the employer, workers’ compensation insurance carrier, self-insured employer, or group fund.