The marriage and subsequent divorce were of course fake. In season one, Callen is revealed to have worked with the DEA (on a joint operation with the CIA, where he first met Arkady Kolchek) and the FBI.

What is the relationship between Hetty and Callen?

Hetty stepped in the save Callen when he was a teen.

Hetty knew much more about Callen's past than he did when the two met oh-so-long ago. Callen had just spent three weeks in juvenile detention before escaping, robbing a storage locker, stealing a car, and then crashing it. That's when Hetty decided to get involved.

Does G survive NCIS?

Shortly after the Season Nine Finale, Callen and the team are revealed to have survived the impact that hit their SUV. Kensi is the least injured member of the team, but becomes extremely worried when Deeks remains unconscious following the explosion.