Over a Language Log Mark Liberman takes a close look at hip-hop versification:
This exercise will clarify why transcriptions of the lyrics, even with bold-face indications of stress, are missing an important dimension. The lines' scansion depends not only on the syllable sequence and on where the performer puts phrasal stresses, but also on the alignment of the syllables with the musical meter. This alignment is not automatic or always obvious — it has artistically-relevant degrees of freedom beyond those available in most other genres of text setting.
He uses 1982's The Message as his example text, with video, sound, and illustrations. Would you believe polyrhythms?