does anyone know if the diplomatic security service (state dept.) poly's its special agent applicants?
To the best of my knowledge, the answer is "no." The Bureau of Diplomatic Security does not list any polygraph requirement amongst its hiring criteria for special agent applicants:
http://www.state.gov/m/ds/career/c8853.htm#qualifications
Moreover, the State Department's polygraph policy mentions no pre-employment polygraph requirement for any job position:
http://antipolygraph.org/documents/12m0250.pdf