Nah, the US would never violate Soviet airspace
There are undoubtedly still strong forces in Siberia. Remember that the US was never the greatest enemy (at least over there, and despite the rethoric).
The greatest danger to Siberia comes from the south, from China.
There has been near constant fighting between Soviet/Russian forces and Chinese forces almost since the communist revolution in China.
These are not mere borderskirmishes but major battles involving troops in division strength and up on either side.
China also has a major force of nuclear weapons mounted on bombers capable of reaching the main cities of the USSR/Russia.