Yes. I'll speak to one aspect of this in particular.

After the failure of the Tienanmen Square democracy movement in 1989, a kind of Underground Railroad developed in China. It was small, but it existed ─ with between 400 and 800 (estimates vary) dissidents escaping the Chinese government crackdown through an organized network and unknown numbers escaping through unofficial channels.

Known as Operation Yellowbird, it united Hong Kong gangsters, police officers and businessmen, the British and French governments ─ even a Baptist minister ─ in a network designed to bring dissidents from mainland China to the coast, where they would be loaded onto boats and dropped off on a Hong Kong beach. A British minister would provide paperwork, and the dissidents would board planes to other destinations. Most did not stay in Hong Kong proper.

Now, this is only one aspect of dissident escape to Hong Kong. I'm sure there are plenty of other stories out there, but I've always found Yellowbird (also Yellow Bird) fascinating, even though it's outside my area of expertise.

Very much yes. At the end of WW2, Hong Kong only had 500,000 people. By 1980, that figure grew 10 times and Hong Kong had 5 million. Now that number is closer to 7.2 million. Immigration from Mainland China is a major factor in Hong Kong's explosive growth. Many celebrities from the older generation openly admit that they swam across the straits that divides Hong Kong and China. The colonial government in Hong Kong had a "Touch Base policy" until 1981, meaning that if you managed to get past the Frontier Closed Area and into Hong Kong proper, you would be allowed to stay in HK. If you were intercepted before that, then, like the baseball metaphor suggests, you're out.

Hong Kong had a serious shortage of housing for this sudden influx from the mainland (and still does). Most of these new immigrants lived in shanty towns, while people associated with the Republic (and did not follow Chiang Kai-shek to Taiwan but came to HK instead) mostly lived in their own "exclave" in Tiu Keng Leng. Those escaping from both Chinese and Hong Kong authorities would find refuge in the famous Kowloon Walled City, where the British laws of Hong Kong didn't apply, since it technically belonged to China.

The British turned a blind eye to these developments for the most part, until a devastating fire in 1953 burned the shanty town of Shek Kip Mei and left 53,000 people homeless. This forced the colonial administrators to find ways to accommodate the new immigrants, which led to HK's first government housing.

At this point I should say that Chinese citizens fleeing from Communism did not just integrate into Hong Kong life, they shaped Hong Kong life itself. All the talents of China considered too bourgeois and faced prosecution there eventually concentrated in Hong Kong since it was one of the few liberal Chinese-speaking areas in East Asia. They were the ones behind Hong Kong's explosive growth and put the city on the map.