Are certain NOPAC routes reserved for military use?
A local air force reserves chunks of its airspace as they see fit. But it never applies to publicly published inter-FIR routes. So the answer is no.

From Fundamentals of Air Traffic Control (on Google Books):



The routes stay out of Russian airspace, why that matters? Russia has a history of limiting civilian traffic through areas of their airspace. Like parts of the arctic circle, which only started to relax in the past decade or so.