I would consider that discrimination, unless it applied to all religions. e.g. if you're a Catholic, you can't interview a Catholic, etc. But even that I don't think would legally fly because (IANAL) I believe religion is a protected class.

It's not discrimination because it has nothing to do with whether Mormons are hired. It has everything to do with who has a say in hiring them. BYU grads can still be hired, they just have to be hired by someone who isn't going to bias their decision with their personal beliefs.