How does Kimimaro's Kekkei Genkai work?
Kimimoro's Kekkai Genkai isn't like Gaara's sand.  Gaara's sand can go underground, smash the rocks, and use the hardened minerals from the local rocks and incorporate them into his sand.  Kimimoro doesn't seem to do this at all, but rather his bones and chakra system is all internal.  

I think this is evidenced not by what he does but by what he doesn't do. In his battle with Gaara which is clearly his most pressing battle (since he dies in it) he transforms multiple times, he uses his spine whip, and does a number of other jitsu but never absorbs from his exterior surrounds while Gaara clearly does.