Do you have to know facts about the poet?
A basic understanding such as their childhood, life and certain things depending on the poet are needed. It's also nice to know actual quotes from the poet like their last words are great.
If you can use a part of their life in reference to their poetry, then it can be useful, e.g. for Sylvia Plath you can say that Poppies in July relates to her struggles with depression. But don't worry about that kind of thing very much, the examiner is more interested in your personal response (and interpretation) of the poem and quotes.