Where I went to school, usability and interface design was part of the computer science program. It was a requirement for my degree.
In games work, I don't generally see people specialized in UI. I worked with one artist who specialized in UI, but he seemed to be a very unusual case; all other UI art in game projects I've been on was made by artists whose primary focus was other things besides UI. It tended to be a minor task relative to other things.
From the programming side of things people had varying levels of comfort/skill with the user interface side of things, but generally the people with the most facility with UI were called "tools programmers", which is descriptive of the kind of work they do. Development of tools probably has the bulk of UI work in a game project, but it comes with the grain of salt that most tools are also internal, so you don't really get the same kind of approach as for a program that you present publicly. There's UI for games, too, but this is a task that is often underestimated and poorly implemented, and sometimes you want a game's UI to suffer in usability for the purposes of the gameplay too.
What I'm saying is that games might not be the best field to search for such a person, but I don't know what your needs are. Presumably you need some sort of intersection between UI graphic design and UI programming, and probably there's some people out there who can do both (though I think a pair of people is more common). I think you'd be more likely to find such a person in web-oriented places, than games.