Can presented papers at conferences be listed in the reference section of Research Statements? I have some presentation in conferences, which have not published as a proceeding or in a journal. I would like to know whether it is customary to put presented papers in the reference section and cite them in research statement?
The references for a research statement follow the same customs as references in other academic documents.  So yes, you can cite conferences.
Is it common to cite conference papers in a PhD?