If the answer is "yes" to the qualifications below...then Yes they can perform the service:
The services of an NP may be covered under Part B if all of the following conditions are met:
• They are the type that are considered physician’s services if furnished by a doctor of medicine or osteopathy (MD/DO);
• They are performed by a person who meets the definition of an NP (see subsection A);
• The NP is legally authorized to perform the services in the State in which they are performed;
• They are performed in collaboration with an MD/DO (see subsection D); and
• They are not otherwise precluded from coverage because of one of the statutory exclusions. (See subsection C.2.) 2. Incident To If covered NP services are furnished, services and supplies furnished incident to the services of the NP may also be covered if they would have been covered when furnished incident to the services of an MD/DO as described in §60.
http://www.cms.hhs.gov/manuals/Downloads/bp102c15.pdf
(Section 200)
As for who receives credit...
If the physician performs the E/M, I would credit the physician; even though the NP is peforming the injection. It almost sounds as if the MD is utilizing the NP in a nursing capacity.
My opinion...not a cost effective way to use a NP.