In a timeline where the Republic of China won the Chinese Civil War either before (blocking the Long March) or after World War II (crushing the Communists in Manchuria)?, would Hong Kong still be a stronghold of opposition and dissent against the mainland?
Honestly this depends on a lot of factors.
Firstly, Hong Kong only really started on the road of representative democracy in the
1980s after the Anglo-Chinese agreement on the transfer of Hong Kong. So conceivably, had the Republic of China won the Chinese Civil War (either in 1936 using the Long March POD you have or in 1946-1947), then the
Temporary Provisions against the Communist Rebellion would likely never even pass (or if they do then they expire in 1951). At which point we have a
Republic of China that has:
* a directly elected Legislative Yuan (as the legislature) with 3 year terms
* a directly National Assembly (whose purpose was to elect the President of the Republic and amend the Constitution) with 6 year terms
* a President of the Republic elected by the National Assembly with a 6 year terms (and a max of 2 terms)
* a Premier/Prime Minister who would be nominated and appointed by the President after the Legislative Yuan gave its consent to the nominee
.....meanwhile Hong Kong continues to be run in the 1950s, 1960s and 1970s by a Governor appointed by the British with an advisory Legislative Council consisting of other official government members (appointed to their positions) and unofficial members who were appointed by the Governor. So unless a lot of things change and the Republic of China in victory becomes a one-party KMT state, then as the 1970s roll around a few things are going to happen:
1. Portugal's Carnation Revolution (presumably not butterflied away) will result in a Portuguese government which in 1974-1975 will begin to propose handing over Macau to China.
2. The Lease on most of Hong Kong would be coming to an end in 1997 and the British will likely begin talks with China in the 1970s and 1980s on resolving the issue. As In OTL the British may press for an extension of the lease or continuation of British administration under Chinese sovereignty but I doubt a Republic of China that won the Civil War in the 1930s-1940s and had continued under the 1947 Constitution would agree to either of those options and so we get a handover in 1997.
3. Any changes the British make to the local governance of Hong Kong in the 1980s will likely only have the effect of having Hong Kong catch up with 40 years of Chinese democracy.
End result is that Hong Kong is very unlikely to become a special autonomous city but rather, it and Macau will become municipalities in Guandong province, though there may be special local provisions concern language and contract law and such.