I should have made it more clear in my post that my curiousity was about the question(s) as applied to all NPs, not just to this specific instance. If an NP is qualified to be a billing entity (not all NPs are so qualified) and is billing as the billing entity, and if they are non-par with a carrier, are they free to charge whatever they wish - as a doctor is? At this point, this is a rhetorical question, not a real question.
Two of our clients have an NP (one for each provider), and I researched the issue of how they could/should bill for their services when they came on board. Both NPs are qualified to bill on their own, but both are billing under the name of the supervising physician. Since neither NP is billing on their own, it didn't occur to me while researching the issue to find the answer asked in my first paragraph above.