Dear René-Louis,
You should definitely talk with VOR Holdings. Actually, the CAAC written exam is the very least of your worries. You can take the written test over as many times as necessary. The company interview, company sim check, medical and the caac check ride are the hard parts. VOR Holdings has study information on its forum that provides each airline's sops, training guidelines, reports from previous pilots that have taken the check rides. They also support you through the interview and help you all the time that you fly in China. I know many other guys that came to China that were left with little or no support. Their lives were not fun.
Good luck! I hope everything goes well for you.
I'm glad that you had a good experience with VOR Holdings, but that does not appear to be the consensus view on this forum, or any other. Have they done away with the exclusivity clause in their contract? Have they ever got a good answer for tax treatment of U.S. citizens?
TP