Yes of course, all intelligence agencies have paid and non paid informants, no different than the police or journalists and they could be of any citizenship.
Anyone who lives with another alias or identity will have psychological issues as to re-entry and/or their original or true identity. The longer they use the alias, the more likely this adjustment phenomena on return may have negative impact . In theory under cover police officers are supposed to be pulled after so many months to prevent overly identifying and attaching and becoming sympathetic to and identifying with the people they are reporting on- it is a variation of Stockholm Syndrome.
The ability of detaching oneself from their alter-ego or assumed alternative identity without negative phenomena experienced, depends on many factors including how long you engage in that identity, how much demands were placed on you emotionally, and how long you have been separated from your family and loved ones in the real world.
People with no support group of friends or loved ones to come back/return to after living as an alter-ego do not do as well re-entering as do people with such connections. Each operate has a handler who is supposed to monitor the psychological effects and pull them If problems develop and serve as the anchor back to the real world. A skilled handler knows what signs to look for and when to pull back so to speak on the leash and inversely know when to let the leash stay loose.
The only way you probably would not have any negative side effects with identity re-entry issues is if you were a pathological liar or psycho-sociopath . To be able to detach your emotions and ego from what you do and keep them distinct is very problematic even for the best of us. This is why what you see in movies and on t.v. is b.s. It is not that glamorous,. Often its tedious surveillance or research. Sitting and analyzing weather and how it will effect cycles of production or impact to create famines, draughts and movements of population is not glamorous.Identifying risk patterns and liability exposure is not glamourous. Tracking cyber security issues is hard work requiring intense focus. No one is jumping from buildings. They are probably an anonymous employee id no. in a portal.
Keep in mind the CIA is just one of hundreds of intelligence gathering agencies in the US. Each segment of the US Armed Forces has an intelligence branch, The Justice, Treasury, State, Home Security, Interior Departments have their own. Every police force and enforcement agency at a federal, state and local level may have one. Many do not share information causing a lot of counter productive work.
All countries have agents who try get information from other countries, friendly and not so friendly. The majority of intelligence gathering deals with obtaining trade, industry and intellectual property secrets by payments (bribes) or by extortion through having compromising information on someone. Just ask Donald Trump what Vladimir Putin has on him. Here's a hint, you think Melania was just a model. Her Daddy was way up high in the Commie Party. You think it was a coincidence she found him? Lol. She was a high priced escort whose job was to get business secrets out of his big mouth. I should send you the pictures of him being spanked in his diapers.
We all have skeletons someone may try use against us if its to their advantage . In my case there are compromising pictures going around with me and Katherine Wynne. Hey I was Jethro Bodine and she was Jane Hathaway. It was all innocent at a Halloween party.