99.9% of the time the zero to hero pilots are okay. Unfortunately the .1% will bite you. I've had to literally teach some of these pilots how to fly on the line. When the crap hits the fan you can no longer be single pilot or teaching some 250 hour pilot what to do. Yes, there are checklists to follow for most emergencies, but some situations are outside the checklists. Also, as a captain, I think it is best to be the non-flying pilot (NFP), during emergencies (studies back this up as well). I need a pilot in the right seat who can fly the airplane in difficult situations while I troubleshoot.
There have been several accidents and incidents already where poor training and lack of experience have been contributing factors (Pinnacle Airlines crash comes to mind).
In the two emergencis I have had I have been fortunate to be flying with FOs who had a solid background and could handle the airplane while I coordinated things (both had been CFIs and 135 pilots). In one case the FO was doing such a good job flying that I let him land it rather than taking the controls at the last minute (smoke in the cockpit). In the other case I exercised PIC authority and took the controls while being vectored for the ILS after all the checklists had been run, weather checked at possible airports, coordinate with ATC, etc- single engine, night approach to minimums, in a snow storm, braking action fair.