student rate at conferences
Yes.

The purpose of student discounts is to encourage people with a limited income and limited funding to participate.  Recent graduates are in that category.

Most students presenting at conferences are PhD students.  Usually, PhD students are not sure when they will finish their degree.  It's perfectly normal for a PhD student to register for a conference as a student, and there's no reason to change their registration if they happen to graduate before the conference occurs.

I've never seen a conference verify any information I have sent to them.

(Conferences are not publications in my field.)