It's cool regardless, IMO. No matter where all that line art comes from, it still takes a special eye to put it all together in such a unique way. It's always got an edge, always solid, always tight, each one with it's own unique character.
To answer your question, sources vary per individual piece. I think some of Connor's more interesting designs use a combination of line art, ornamentation and illustrations from a particular artist.
i always wonder how much of these type of images is actually handdrawn and how much is lifted and placed and how much is digitally created. if its all handdrawn...really rad, part hand drawn part other sources...very cool, all digitally created from found stuff/digitally drawing...eh, not so cool.
like the colors though.