Aw…You sweet talker you. I bet you say that to all the girls.
Is there an ethical issue? Well, if your son has already interviewed, he’s already applied, so hasn’t that ship sailed?
Very often, the answer to ethical issues is disclosure. Yes, he did X, Y and Z, and yes he’s you son. Will that influences his chances? Maybe. In what direction? Hard to tell, especially as we would be comparing to some counterfactual universe. It is what it is.
I’ve interviewed a couple hundred students for MIT. I have never been asked to rank applicants. I have never gone out and ranked applicants on my own. I sure would not tell one student where they ranked with respect to another, especially in the same cycle. That is wrong on so many levels.