In an interview with a potential PhD supervisor, is it ok to refer to papers published by a different academic, or should I mainly talk about the potential supervisor's papers?
There's no ideal answer here—it really all depends on the ego of the potential supervisor. A good potential advisor not only teaches her students, but is willing to learn from them as well. If you know something that touches on the topic you're talking with a potential supervisor about, I see no reason not to mention it. You're demonstrating familiarity with research in the field, and that shows you're willing to put in the work to learn, which is an important part of becoming a good researcher. I'd prefer that a candidate tell me what she knows, rather than hide it for fear I'll be mad about the fact that she mentioned someone else's work.