Factoring that "all fescue course" is one of the major reasons why they got the US Open and is a crucial part of their marketing plan, I highly doubt that anyone even considered using different grass.
The green is butted against the hills on the eastside and as such does not get a lot of sun in the morning. If it was located in the middle of the property, it probably would have been okay, but the lack of consistent sun kinda forced the issue. Based on how well the greens are growing on other holes in the same location (#13, #7, #8), I believe the new green will be just fine after the remodel.