No.
@Eur:
Neutral Powers: When a power is not at war with
anyone, it is neutral. Powers that begin the game
neutral, such as the United States and the Soviet
Union, aren’t initially part of the Allies or the Axis. The
Axis powers are on the opposite side of these neutral
powers, but they are not yet considered enemies.
While a power remains neutral, it operates under
even tighter restrictions. A neutral power can’t move
land or air units into or through neutral territories. It
can’t move units into or through territories or onto
ships belonging to another power or use another
power’s naval bases, nor can another power move
land or air units into or through its territories or onto
its ships or use its naval bases.
Now maybe you are thinking they can declare war on Japan and then move into NW Persia? No, because:
@Eur:
Due to its separate treaties with Germany and Japan, the Soviet Union is in a unique position in its relationship with
the Axis powers. As a result, if the Soviet Union is at war with Axis powers on only one map, it is still under the
restrictions of being a neutral power (see “Powers Not at War with One Another,” page 15) on the other map. In other
words, a state of war with Japan lifts those restrictions from the Soviet Union on the Pacific map only, and a state of
war with Germany and/or Italy lifts those restrictions on the Europe map only.
HTH