Desde wowwiki:
It is a common misconception that Sword Specialization can only proc off of normal (white) swings. This is not the case and is likely confusion over Windfury Totem. Windfury only procs off of normal (white) swings. Sword Specialization procs from all damaging attacks, including special attacks.

It counts Whirlwind as a single attack for chance of proc.