Tennessee does not provide special admission rules for government attorneys licensed in other jurisdictions.
However, Tennessee provides a Tennessee Multijurisdictional Practice Rule (MJP) within its rules of professional conduct. Comment 16 to that rule provide for an interpretation that exempts government attorneys from the unauthorized practice of law.
Please also see the Tennessee Bar Reciprocity page to view the requirements for Admission on Motion, and the Tennessee Pro Hac Vice page to view the requirements for admission to a particular proceeding.