Hong Kong and China are separate* entities when it comes to immigration/visas. A China visa is not valid in Hong Kong, and a Hong Kong visa is not valid in China. So you would need through the TechTAS to get a Hong Kong employment visa. So good for insisting!
About half a dozen years ago an Australian risk management(!) expert came to Hong Kong several times to teach at weekend seminars, which he did without the relevant visa. Someone shopped him. He enjoyed a 2-month stay in one of Hong Kong's prisons before being kicked out (probably "excluded" for 3 years too). Perhaps he got it harsher than others, but it's still not worth the "risk".
* Except, obviously, China can say no to certain people entering Hong Kong, and the Hong Kong government will obey and block them.
Last edited by DragonSoul; Nov 15, 2018 at 1:20 am