I think it would be really difficult for an Fi dom to be a narcissist. Because narcissists don't have a sense of self--they are pretty much just their superficial persona and their relationship with other people (how others see them and what they can get others to do) defines who they are.
They are almost incapable of introspection. Literally incapable. And Fi doms are some of the most introspective types.
And most Fi doms are pretty in tune with themselves and their deeper feelings (something narcissists struggle with), and many don't even manage a persona very well.
So I really doubt there'd be a propensity in the type to correlate with NPD. I would guess more likely to correlate with an Avoidant personality or possibly Schizoid Personality disorder as Fi is also thought to be highly idiosyncratic. Maybe something like Histrionic, but I think that's more stereotypes about Fi that are projections, as Jung didn't describe Fi as being Histrionic.
He did say that unhealthy Fi types can become paranoid and suspicious of others when their Te gets weird, which is probably more like Avoidant or Paranoid personality disorder.
EDIT: Ok Jung specifically said this (idk if he said anything else about disorders) about Fi doms:
"Such a development must end in exhaustion. The form of neurosis is neurasthenic rather than hysterical, often with severe physical complications, such as anemia and sequelae."
So he said it's not hysterical, but..."neurasthenic" which is: "an ill-defined medical condition characterized by lassitude, fatigue, headache, and irritability, associated chiefly with emotional disturbance"
So basically an unhealthy Fi type would be prone to exhaustion, irritability, fatigue, and headaches and other symptoms of emotionally fueled issues (according to Jung).
And while you can't really say a type is prone to one mental disturbance over another, Jung's description here touches more on Depression...which is something I've seen many INFPs struggling with over the years (and tbh I think it'd be more honest to suggest INFPs may tend to be prone to depression--though again, people want to separate type from mental health issues), so I'm inclined to think that if there is any correlation it would be moreso what Jung and observations describe, rather than NPD...which really doesn't even make sense in the theory.