I have several friends working in Chinese run airlines and I myself worked for Hainan for one of its side companies.
Hainan basically runs Hong Kong Airlines and Hong Kong Express, so read the threads on those companies and it should give you a fair idea about Hainan.
I also know some friends that applied to Hainan and the process takes a LONG time. 6 months +. Lots of paperwork for the License, and Hainan also takes a long time due to the "mainland factor"
If you do work for Hainan or any Chinese company, expect no rights as a worker. Expect your pay to be docked if you have a sick day even if your contract says you get them, expect chain smoking in the cockpit, expect no CRM, expect corruption, stupidity, lies, false promises; expect to be shafted in some way or another. They will give you promises which will not be honored.
Hainan and all Chinese companies have a long way to go to get foreign pilot recruitment right.
Good luck