What about Hongkies, they also use Lam etc because of colonial slavery?
The Cantonese have their own phonetic system. Instead of four main tones in Mandarin, they have six.
Hong Kong is part of Guangdong and has been so for thousands of years. One thing about being Chinese is that provincial identity is stronger than national. A person would consider himself Cantonese first, Chinese second, and if he/she is ultra-traditional, all others are "barbarians" or 鬼. Discrimination against those from "outside of the province" (外省人) and don't speak the local "dialect" is traditionally strong. I put dialect in inverted commas because many are mutually unintelligable and it is not a dialect in the European sense of the word.
The Fragrant Harbour is unique in that on top of the Cantonese base, there were also mass migrations of people from other provinces due to Civil War, Great Leap Forward, Cultural Revolution and what not. Hence you have the Shanghaiese, Hokkien, Teochews, etc thrown into the Cantonese pot. For these "migrants", British rule of law was better than Chinese "rule by man" - regardless of whether that man is the Emperor, Yuan Shikai, Mao Tse Tung, Deng Xiao Ping or worse, Lee Kuan Yew.
"Lam" is the Cantonese way of spelling 林. The late founder of Lai Sun, a listed company here, was a Teochew. His surname was spelled "Lim", but his son's surname is spelled "Lam". Like I said, discrimination against 外省人 is strong and one way of avoiding it is to spell your name in the Cantonese, Fujian or whatever way if your forefathers were migrants from another province. Another way is to speak Cantonese like a local. Or bypass it by getting your Hokkien brothers together to form your own clan association and help each other out in business.
The Mainland is trying to get rid of this "provincial" mentality and replace it with a national identity and one way is through Mandarin and Hanyu Pinyin. Subdue is attainable, but to eliminate it, is I think impossible.