Nikon just refers to it as 'reinforced glass' which suggests to me they are not using Gorilla Glass (tm) but maybe something very similar that they didn't have to license.
The screen is the exact same dimensions as the D600 and likely has a similar construction in that the glass is essentially part of the back plate. The issue is if you scratch the glass on the D600, you have to replace the entire back - which could be costly. If the D7100 is the same, you definitely want an LCD protector.
I suspect the D600 GGS ones should work on the D7100 given the dimensions.