One of the Oneworld's rule dictate that member airlines can only give EQM if the carrier/marketing carrier is another OW airline, the only exception is if the carrier/marketing carrier is a wholly owned subsidiary like QF/JL with Jetstar. Or, the extreme case like Qantas and Emirates where exception apply.

BA's earning chart gives the detailed illustration on which case one can earn EQP/EQS/EQF...

Even if you purchase a CZ operated BA coded flight, it would only benefits BA Executive Club members to earn the elite qualifying points, but not for any other oneworld flyers. If you bought the flight operated by CZ in CZ code, you will not get any EQP, but you might get award miles according to BA Executive Club rules, which needs to be updated soon.

So, as long as CZ is an independent carrier, oneworld flyer would not benefit from its relationship with AA and BA, if one is to doing the elite member qualification trips. Remember, any CZ operated domestic flights, one can not buy it in BA or AA code unless it is a connecting flight to BA or AA codes intercontinental flight. If CZ truly want to tap into the vast oneworld elite frequent flyer pool, it needs to join oneworld, or lobby AA and BA to change the current oneworld rule (which would mean the death of the alliance) or do a QF with its exceptionalism.