If the non-Chinese Singaporians were represented as normal people walking down the street in the film, but the film just didn't focus on them, I think it would be fine. But they are present, in non-speaking roles, in servant positions. It would be better if they just weren't present.
Overall, I enjoyed the movie, but I was uncomfortable with this flaw and the representation of the lone homosexual. Everyone has partners, but not him. Why not at least give him a date for the wedding?
This is no better or worse than most American romantic comedies, which doesn't excuse the misrepresentations. There is, of course, enough cultural tension for the film, which is well played, and it has a fine balance between romance and comedy. I'm a sucker for romantic comedies in general, but these flaws did take away slightly from my enjoyment.