The SAS are definitely there, the Beeb even got a leaked pic of them not that long ago:
The Syrian authorities also nicked a couple of SAS forces who they found crossing the border from Iraq a while back, but they released them back to us after some high level negotiations.
US Special Forces have also raided targets in Syria from time to time, Delta Force did a raid back in May 2015, I wouldn't be surprised if the KSK have been in there too after the attacks.