I'm watching Oliver Stone's Untold History of the United States and he mentions that the U.S. had dropped napalm on Greek villages. Knowing what I know about the Vietnam brutality, is there any corroboration to this magnitude of disgust?!
No, there isn't any corroboration to this claim.
During the culmination of the Greek Civil War in the form of the dual battles of Vitsi and Grammos in the summer of 1949, the RHAF (Royal Hellenic Air Force) dropped napalm on DSE (Diokratikos Stratos Ellados) positions in what was to become the heaviest bombing of the war and ultimately lead to the near destruction of the insurgency. Napalm during this particular conflict had first been used the year before at the same place mentioned above, the Grammos mountain. While it had little effect in 1948 due to its deployment in very few numbers, This napalm, and much of the military assistance provided to the Greek government at this time in 1949, came from the United States in the form of the American Mission to Aid Greece as part of the great Truman Doctrine to contain communism.
The answer is thus no. The United States did not napalm Greek villages. The Greek themselves certainly did napalm villages which were under control of the DSE or supported the DSE, with the U.S. providing the napalm through the AMAG.