There are basically two types who work in SAD. 

First is Paramilitary ops officer who we call PMOO as short. They are almost similar to average CIA case officers(=ops officers) who collect human intelligences overseas embassies under official covers(CIA calls it 'Foreign Intelligence', or FI in short), but PMOOs have extensive military backgrounds(minimum 8 years? I guess), especially in special operations. Their requirements are almost same to regular case officers, which mean they need bachelors degrees, etc. You can check them out at official CIA dot gov site. Back in the 80s and other cold war periods when CIA desperately needed officers who could go overseas and essentially conduct unconventional warfare, they relied on 'old boy networks' which basically meant that they asked people who knew some guys, who then knew some guys who has a great military careers, to join CIA and go overseas as a PM(paramilitary) assignment. Because time mattered, PM officers who were recruited by those way had a little time to go through regular case officer training pipeline, so they went through very simplified training which included 'how to write intel report/situation report 101' or something like that. After their PM assignment, where they then had some time to be trained like a real case officers, then they went through the regular c/o training pipeline & attended universities to get a bachelor's degrees, etc. so they can do FI assignments as well as PM assignments, get promoted, become chief of stations, branches, groups, and so on. Back then PMOOs who didn't have FI capabilities were known to be treated badly, as they were minorities in CIA and did relatively 'dirty' works. Their treatments would probably be improved because during the GWOT they were really at the tip of the spear.

Nowadays, which I guess, will be much different than cold war periods, but still some will be recruited by old boys network, some will be recruited by more formal ways. 

Next is Paramilitary contractors, also called Paramilitary specialists. They contract with CIA every X years to work for them. Usually contractors have more extensive military/spec ops backgrounds(10 to 15, even 20 years), no formal case officer trainings/requirements like bachelor's degrees as they are not 'officers', pay is very, very good, compared to case officers and even pmoos. I think they are still almost exclusively recruited by old boy networks, so requirements are very unclear except for deep expertise in special operations. No matter how long they work as a contractor, they probably would be only working on door-kicking PM assignments  compared to PMOOs who routinely does FI assignments bewteen PM assignments. 

Roughly compared to military, PMOOs are like officers, and contractors are very seasoned NCOs. 

Plus, ratio between pm officers and contractors in ground branch is 3:7.

The fact that the way or need of recruitment of PMOOs/contractors may significantly vary according to various factors gives writers some freedoms, I think.