As usual, Cookie raises a number of good points.
Last night I went back through the various ASA histories that I have relating to the Korean War, and discovered that ASA Korean linguists were indeed used for a few "special projects." For example, a number of ASA Korean and Chinese linguists were used as part-time interrogators, where they focused on questioning Chinese or NKPA POWs who served in communications or cryptologic billets. The interrogation reports that they produced were not, however, fed into the normal interrogation intelligence reporting system run by the Allied Translation and Information Service (ATIS) because of the sensitivity of the product. ASA personnel were apparently also used to translate captured codebooks and other documents relating to cryptographic subjects that fell into U.S. or Allied hands. ASA personnel were engaged in a number of other highly classified intelligence collection operations during the war that have not been declassified yet, but which were mounted from the relative safety of South Korea.
But generally speaking of the Korean War, the former ASA and USAFSS personnel that I have spoken to all seem to agree that the highly classified ASA operations, coupled with severe linguists shortages throughout the war, would seem to mitigate against using these highly trained personnel for behind the lines operations.
Cookie knows far more about ASA operations and special projects in Southeast Asia than I ever will. He mentioned James Davis, an ASAer who was the first American soldier killed in South Vietnam. For the record, Specialist 4th Class James Thomas Davis of Livingston, Tennessee was killed on December 22, 1961 along with nine ARVN SIGINT personnel while serving as a radio research advisor with an ARVN mobile HFDF team near Saigon. Davis was killed by Viet Cong small arms fire after the truck carrying his ARVN team was ambushed while trying to track down a Viet Cong radio transmitter with a portable AN/PRD-1 HFDF set. This was one of the first instances of American SIGINT personnel providing advisory assistance to a foreign intelligence service.