Not that unusual. But kind of a pain in the ass for early career mentored grant applications, because some of them stipulate that you can't hold an academic faculty position to be eligible, and you'll have to explain it to them that this is just the way your employer does it. At some places, Instructors are full-on independent faculty with their own start-ups, etc. At others, you're sort of appointed there because you're in a no-man's-land between trainee and faculty, and they don't have provisions for it. It's ambiguous.
Often, Instructor is the highest rank that a chair can appoint someone to without approval from the University or Hospital Board of Regents. Above that, they may stipulate that the hospital to undergo a formal posting and national search, followed by screening the applicant's CV for suitability for the suggested rank. Tenure tracking, where available, further complicates things. I'm not aware of any place where Instructors have any formal position on the tenure track (other than as a foothold to get appointed Assistant Professor, upon which they can move in that direction).
