I believe he hid his secret life well, so not sure a psych evaluation would have worked. He was obviously good at his job.... professionally speaking of course
Psych evaluations would be unlikely to find some like Colonel Williams. The biggest "give away" in his military career file is that he has no obvious weaknesses. It is unlikely that someone in his position has no character weaknesses, so it implies that the military did not know what the weaknesses were.
The fundamental problem with using Psych Evaluations for fitness for employment is that the tests are easily gamed. The best liars score the best. The best liars are sociopaths, and usually represent very bad hires. The "honest employee" tests, and the MMPI test have been repeatedly discredited as employee testing tools, because the tests can be easily gamed by an intelligent person.
In particular, the psychological community routinely recommends that the MMPI test should only be used for diagnostic purposes, and not for employee screening purposes. A sociopath can easily game the test, and is often successful at gaming trained interviewers in a "one on one" setting.
Myself, I believe the best indicator of character flaws is efforts to know people and know their weaknesses. Knowing a person as part of a community frequently gives the best warning about problems happening and about to occur.