The original question addressed: Schizoid personality disorder and a Schizotypal personality disorder.
Schizophrenia was not mentioned and is something quite different...unless the original diagnosis was wrong, and that's not at all unusual. People act differently at different times and some people have multiple problems.
Yes, the 2 personality disorders mentioned can mimic parts of Schizophrenia and might even approach it in some ways, but they aren't the same thing. Check the current DSM for the checklists. WARNING: reading the DSM will make you crazy when you start thinking YOU have all the symtoms.
Mental health diagnoses are frequently wrong or incomplete. I have been working face to face with individuals with all sorts of disabilities for 29 years and part of the job is reviewing their medical records. Heck, straight out of grad school they had me reviewing Social Security disability claim files for two years to identify individuals who might have the ability to return to work. My job was to decide which ones to send out for the field offices to contact.
In a nutshell, it's fascinating to read 5, 10 or 20 years or more of psychological evals, psychiatric evals and hospital discharge summaries (among other things) and see the variety of diagnoses one person can accumulate over the years. I realize that in many cases all of the diagnoses are correct at the time they're made, but in many others it takes time to figure out what is really going on.
The personality disorders, including the two mentioned initially, can be just as difficult to diagnose as the more 'serious' and debilitating ones like Schizophrenia. Not that a personality disorder can't foul up your life, it's just not the same as a psychosis. And yes, thousands and thousands of people hear and see things.
The folks with a diagnosis of Borderline Personality are well known for getting a different diagnosis every time they are seen by someone new. It just depends on how they're acting and feeling when they're seen.
Without seeing the original report I wouldn't hazzard a guess about the accuracy of the diagnosis or the ability of the individual to safely handle guns.
I recommend a new evaluation if the person is unreliable and untrustworthy. If this is more or less an academic question concerning a diagnosis on a military form from 10 or 20 years ago I wouldn't worry about it much.
My personal opinion is...you or the immediate family and friends already know if this person is dependable or behaves too erratically to be trusted. That's what the evaluating psychologist or psychiatrist is going to ask you anyway if you participate in the evaluation. If you don't participate, well then who knows what the person will tell them and what the diagnosis will be based on the BS they're told.
It's late, I'm rambling on. That's enough for now.
John