@mzimmerman ...
Actually, it is possible for someone to be enrolled as a Teacher and Student in the same section of one course. For example, I was initially enrolled in my sandbox course as a Teacher, but then I manually enrolled myself as a Student via my e-mail address. I refreshed my screen, and now I'm both a Teacher and a Student in the same section.

I had a situation a few years back where an instructor wanted to see exactly what a student would see in a third-party LTI (Turnitin, if I recall). But, when the instructor tried to do grading for other assignments that also used the LTI, he was getting an error message because the Turntin LTI couldn't figure out if he was a Teacher or a Student. As soon as we removed the Student role from his course and returned him only to a Teacher, things were fixed and he could grade again.