I had learnt some grammar points where 谁 seems to introduce a subordinated phrase (those people who （谁做谁） ... and who would be 谁, now I was wondering what other functions 谁 could have.
谁 is either "who" or "whom" and nothing beyond. "Whom" happens to not be used often in English. But in Chinese, 谁 as a third person form of "who" is used often.
谁做谁 is on the strange side. But if it is used in some context, it would mean "who is whom" with "whom" potentially has the meaning "role". That is not because of 谁. That's because of 做 can be used as "to take the role of".