I check the link and lyrics.. Why do you think it means “prostitute”... 花儿 means flowers. In the lyrics, it refers to the woman he loves is as beautiful as beautiful flowers. It is a beautiful song. If you have any question on any sentence of this song (kind of like poem almost), tell me please.

The song, 花房姑娘, was published in 1989. Cui Jian was 27 years old then. (Cui is known as a Rock singer.) The communist/Socialist countries were expreicing a new socialist revolution at that time. What a 27-year-old young man wanted to express is unknown. What does 'the girl in the flower house'/'Hua Fang Gu Niang' mean/imply? The mother country, his beloved, or freedom ... etc? The intepretation should be set in the life/society at that time. http://baike.baidu.com/subview/1136286/8678262.htm

在中文里 就没有用花儿来形容妓女的例子

”我不知不觉已和花儿一样“ 这个”花“不是”妓女“的意思。 汉语中的花儿，是美丽的，漂亮的，很多颜色，“”我不知不觉已和花儿一样“是我也好像花儿一样，美丽，漂亮，colorful. 花儿 never be used to describe 妓女 in Chinese.

这需要根据上下文的语境来判断。