That video is a few years old. The whole show was on Channel News Asia a few years ago.
Geylang is the Red light district in SG and its well known for it. Prostitution is legal in SG but the hookers has to register for it and have a health check every 2 weeks. Those hookers are ofcause not found on street corners like these.
What we see on that video is are the illegal ones and its not limited to just SL hookers. The same racket is done with Indonesian, Malaysian, Thai and Philipino hookers as well. They all own several streets in Geylang area.