Probably not unless you modify Seam. You've probably seen this, but....
I already know how to make PDF/A or all the other PDF versions through iText.
But I thought so that I had to somehow modify seam to do that. Thats too much hassle though.
I have found a workaround by getting the content of the PDF through the DocumentStore and using JODConverter to create PDF/A out of the document.
However, you will need to install OpenOffice PDF Viewer extension.