Here is a sentence I've read in an article from BBC News:
According to a new book, South Korean Popular Culture and North Korea, South Korea's government "targeted the export of popular media culture as a new economic initiative, one of the major sources of foreign revenue vital for the country's economic survival and advancement".
I don't know if the title of my question would be the case but I would say "one of the major sources of foreign revenue which is/ being vital for..." because vital is an adjective. However, the original sentence sounds absolutely fine to me, maybe because I've come across sentences structured that way. As an English learner, I would be grateful to get clear rules or any document about this grammatical point.