Well, I'm not sure sociopath quite fits him, though perhaps it does, for he definitely has been trained to ignore empathy. That being said, he is still apparently a shrewd judge of character, which I find in reality does not mesh with complete sociopath (they are often less capable of reading others and more importantly don't give a damn about many things others would. Doakes does care about what he does, and does care, if anything too much, about "stopping bad guys" in a way a Sociopath wouldn't).
However, he is a former Special Ops soldier iirc, who very probably has done some shady assassination-type missions in the name of the US Government, something that people loaded with empathy would struggle with. Even if he didn't assassinate people (there's some evidence he probably did, but certainly nothing conclusive), he definitely has killed people, and he seems to have little to no emotional problems concerning that, so half-sociopath may be entirely accurate, in the end.