It depends on what type of provider is being credentialed. If it is a NP or a PA, yes we may bill claims under the name of a Credentialed provider (if the credentialed provider would be supervising the services). But, I don't think an MD can be supervised by another MD and therefore that restricts MD's from billing under a different MD's name which might also turn out to be fraudulent.
On the other hand, your question about billing under the Group NPI... The bills may go out with Group NPI under Block 33 of the CMS 1500 form. But the rendering provider NPI has to be that of an individual.