Can the Netflix Account Admin see which device has registered?

A friend may have Netflix and I could do that too, but I don't know if my father is pulling which device has registered because none of the family has an I phone X. Yes, the question is a bit strange: I

Yes, the admin can and a lot more.

He will receive an email when a new device registers

So in itself no. However, he will receive an email at his registered address if he has set it up.