I might believe Iranian pilots might be there, but with so few fighters in the Iranian Air Force, I still think they wouldn't expose them in Syria. The insurgents there have shot down a couple of Syrian Migs, can you imagine the news if they shot down an Iranian fighter?
With only 280 fighters of mixed types in the Iranian inventory, still don't believe they are in Syria.
http://www.globalsecurity.org/milita...-equipment.htm