Sally,
In my readings, I've not come across any literature specifically related to autism and polygraphy. Most polygraph operators, in the their brief training, barely scratch the surface of psychology and to make assumptions regarding the suitability of subjects with mental or neurological disorders would be grandiose. I assume those with humility would not consider such a subject. Autistic people possess anomalies in how their nerve cells and synapses organize; the reasons for these anomalies are not fully understood. A polygraph procedure would most likely add stress to the autistic person and produce unreliable results, IMHO.