If they were going to Vegas to play in a show, I can only assume their expenses, including a 1st class passenger (could have been FF miles or Gold/Platinum status) would have been paid for. However, they bought one way tickets and had return tickets on Jet Blue.
I cannot imagine how the FBI would have let these guys go unless they were confident of their itineraries. Then again, the Supreme Court recently ruled terrorists have the same legal rights as other criminals in the US.
Just my google and there are oodles of sites on syrian music and bands etc but nothing specific. They could have been with a church, lots of syrians are not muslims, so that is one thing. But you would think someone would have piped up and said they were associated with them.