Aesop Rock leads the charts in vocabulary size by a wide margin. Apparently he should actually be off the chart in the original report (here: http://bit.ly/1hnnRzJ).
Calculating Wu-Tang's word count from their ten members was complicated. It involved measuring number of words by each member. Their percentage contributions towards the count are shown here. (The author's methodology excluded Ol' Dirty Bastard, Cappadonna, and Masta Killa from the band's count--shown in the chart lumped together under "the rest").