I dunno about that y'know, maybe "hundreds" is pushing it but I'd be confident it's more than dozens. Lot of reports of British, French and Belgium Muslims being found fighting in Syria. Saw an interview with a Hezbollah commander (I'll try finding the video later but I'm a bit knackered atm) saying he encountered a company of 120 or so fighters in Qusayr who were using English to communicate with each other - possibly as a lingua franca as there are so many nationalities in that company, possibly because of a large number of English-speaking muslims now over there fighting, or (as is likely) it's pure propaganda. My point still stands even if it is only a few dozen - look what two men in woolwich did, look what two men in Boston did, it doesn't take much y'know.
How many of the backup from the Gulf states are just those countries opening up their jails and sending the most violent terrorists they have over to Syria (and also Iraq, where the sectarian civil war is also picking up pace) do you suppose?