Should I send quick emails to my interviewers telling them of my results just as a courtesy? (be it acceptance, waitlist, or rejection). Or are they already informed of our outcomes?
They know. No need to contact. If you were admitted, they should contact you. Otherwise they are instructed not to contact you. I think this policy makes sense.
I am an alumni interviewer for another school (not Stanford). I do find out who is accepted, denied and wait listed. It’s always a nice touch when I hear back from a student who I interviewed.