If there is are only a few manufacturers of raws (or only one), then the Chinese authorities would have no problem figuring out who that is. When you're that big, it would be impossible to stay of the radar unless the big manufacturers were protected in some way.
In the unlikely event that China were to close down all the raw manufacturers of GLP-1 drugs (I'm not talking about those who have FDA approval to manufacture, for instance, those used by compounding pharmacies that follow the rules), then manufacturers of raws would spring up somewhere else. The market is too big, the amount of money to be made too great, to suppress raws.
I do find it ironic that the US is currently pressuring China to cut down on the manufacturing of fentanyl precursors considering that the UK and China fought the Opium Wars specifically to make it so that Western powers could sell opium to Chinese folks.