"She’s told me that her role was much more of a recruiter than a gatekeeper "
I haven’t done interviewing myself, but from what I’ve understood from others who have, I wouldn’t say “recruiter” exactly.
More like an enthusiastic, somewhat biased, “information agent”. Mostly they are there to describe what it is like there, in general and particularly as it pertains to a kid’s interests and objectives, and to provide information about the university.
As alums who care about the U enough to do volunteer interviewing for it, they presumably like and care about the university and are likely to share their enthusiasm.
At the same time, most also probably do this work because they like and care about kids. They know the place is not for everybody and probably do not want kids to wind up in the wrong place. They are likely to point out aspects of the university that seem to fit with a kid’s interests, as revealed during their discussion. But I would imagine that, during the course of their discussion, if the kid indicates wanting something that is not there, or clearly does not fit for some other reason, they would provide relevant information about that as well.
They do submit an evaluation report but from what I understand it is given virtually no weight by admissions, ordinarily.
Harvard could possibly do things differently though, I’ve no idea.