I am sort of new to XSL and am developing PDF report in Oracle XML
Publisher. I have my xml data displaying in nested tables where I
have table headers repeating at the top of the page when the table
continue over a page break. I would like to add additional
information in header when the table is printed in the header ONLY on
overflow condition. Is there an XSL:FO attribute or way for me to
determine this condition or is this something I cannot do ?

There is no dedicated feature in XSL-FO, but you can try
to to use markers. Maybe the solution tersly explained here
 http://www.biglist.com/lists/xsl-list/archives/200202/msg01119.html
applies to your problem. You might also want to explore
processor specific extensions, like this:
http://xmlgraphics.apache.org/fop/0.20.5/extensions.html#table-continue-label