If you are talking about someone who's a surgical tech, that is not billable. If it's in a facility, the facility will typically provide that type of staff if needed. If it's office based surgery, then yes, the practice would pay the employee. Just like you would pay a recovery nurse, but can't bill for it. It's part of your expenses.
MD, DO, MBBS, PA, NP and various CNS are all billable assistants. RNs are not unless they are also CNS. The scope of practice for the billable assistants is far greater than RNs and surgical techs. Reimbursement for assistants is in the ballpark of 16-20% of the primary surgeon's if the procedure allows an assist. Also remember that if you have qualified billable assistants, they can also help with discharges, writing prescriptions, etc., so your primary surgeon might be able to be more productive.