Moreover, the British "consulate" in Taiwan specifically states that no Certificate of No Impediment is required to marry in Hong Kong, and suggests that Brits living in Taiwan and wishing to get married actually come to Hong Kong to do it.
Marriage in Taiwan?British Trade & Cultural Office, Taiwan
Here is the US Consulate's guide to getting married in Hong Kong: Marriage in Hong Kong No mention of any documentation except ID/passport (and Decree Absolute for divorces)