Well you can definitely charge for the stress test. As far as charging for a visit this is what I found out: spoke with a couple of people I know, one if which is in auditing, and she states that the NP can bill OV/Consults and does not require SA modifier. She will need to be enrolled with the plans your physicians accept so they will recognize her when you bill. So, if she is enrolled with your plans, they will recognize she is NP and therefore no SA would be required. If not, you'll need to bill with SA modifier. I believe the NPs can see patient's and bill for those visits even if the physician does not see the patient. We have an NP and bill for her.
HTH