In addition, Sue-Wraiths often have few qualities of their own, and are merely sparkles layered over another character in the case of possession. Many recruited Sues, once the sparkles are stripped away, have at least a few traits of their own that may become seeds for an eventually-realized personality. Strip the sparkles out of a wraith, many times, and you are left with well... nothing. In cases of Possession, the Wraith is what an agent aims to remove.

In cases of POV situations and use of dummies... I dunno. Maybe you could seal one inside a golem? But the thing is that in those cases, the wraiths are locked into 'I' and 'You' and may be dangerous for other agents to interact with. Most agents live in third-person POV. A character that exists only in first or second person POV may not even be able to interact with others in HQ.

I believe the reason Wraiths are not recruited is that they require a body in order to do anything. So, if you were to recruit one, you would have to supply a body for it or it would dissipate. Then, once a body was supplied, you would have to find a way to feed it. Since they live off of the emotional energies of the beings they possess, it would be difficult to find a sustained source of nourishment.

Long story short, it is very unlikely that one could be recruited.