I posted a reply same day you asked your question but it seems that it didn't go through.
I was told by the Training Director who gave us the assessment simulator brief that Majority make it, not sure if someone actually gave me this figure or just what I understood, but likely to be 85-90%+ make it through to Fly Dubai, Also he said those that didn't make it had weak CRM/MCC skills and/or very weak performance/Knowledge. Otherwise I agree that it would be an expensive Type Rating without the Job. The course also includes a lot of hours, over 50 Full Flight Simulator hours, to help everyone succeed. It's also understandable that Fly Dubai wants Good pilots, who will eventually become Captains and not just career first officers.
One of the guys who passed the assessment and finished the Type rating and got the job, had been out of flying for 9+ years, he did his flight review and made it through the Type Rating and will soon be in the right seat.
Hope that helps.