Just found some more info. see:
http://www.ias.ac.in/sadhana/Pdf2004Jun/Pe1131.pdf
On studies between egr at 0% and 21% open at different loads, show temperature differences of no more than 20 degrees C. to the exhaust gases. The effect on the combustion temperature therefore would not increase to over 900+ degrees C, that would do damage, unless there were other problems.
Egr systems also cause an increase of particulate matter(soot)that can have a detrimental effect on the engine and of expelled exhaust gases.
Russ