I believe Nikon makes the glass for their cameras, and other stuff also, and I'd bet they did for the Japan made scopes, but id also bet the Philippines made Nikons ran what ever glass was most cost effective.
Their glass division is called Nikko. They also are one, or at least were, of the suppliers to the Germans. They make very good glass. So what I've gathered. Rumor too, Leupold also sources/sources some of their glass from them also, but they never confirm where exactly, they get their glass, but it's not hard to figure out. Their is only one optic glass maker left in the US (Meopa), there is Nikko in Japan, a few in Germany, then there is the cheap Chinessium plants and the two in the Philippines.
Hakko was once one of the top producers, but they got gobbled up and no longer make sport optic glass.
Far as Nikon went, I'm 100% certain they used their own glass. You can tell by simply looking through them. I have mid grade buckmasters, the glass in those is very comparable to the mid grade VX-111s and VX-3s from Leupold. They could get away with better glass because they owned the entire process from start to finish.
Then...there are my Monarchs...which are a large step above the buck masters. They are fantastic scopes!
Even the cheap P-308s glass is better then any of Leupolds low end scopes, at half the price.
But I digress...who really knows. Nikon didnt advertise their sources anymore than Leupold, Vortex, Zeiss or anyone else besides Schmit and Bender and IOR...which both prominently tell you they use Schott Glass.