How do the two sides keep a resistance from coming out of the neutral zones?
It looks like a big chunk of Russia is still free, but how much they can do depends on if Stalin managed to evacuate industry beyond the Urals.
Dick never fleshed out a lot of these things - wasn't essential to the narrative and the ideas he was trying to work with, it seems.
But as far as the Rockies neutral zone is concerned, it sounds like both Axis powers rely on a combination of puppet governance and heavy intelligence infiltration there to keep any resistance movement from reaching any serious threat.
We know even less about Russian Siberia. But it's probably not far removed from what Calbear paints in his Anglo-American-Nazi War TL: one or more rump Soviet or post-Soviet states, forced to send heavy shipments of raw materials and workers to the Reich and possibly Japan as well.