According to the latest from netkas.org, they've got the Radeon HD 6970 working.
September 3, 2011
Got 6970 working!
September 03rd 2011 Posted to ATI, Apple, Lion
It's only for Lion.
1) get 10.7.2 11C48 beta (from imzdl.com for example)
2) Install all ati kexts from update with pacifist (or install whole update)
3) download this file – http://rghost.ru/20320401 and copy it to this folder – /System/Library/Extensions/ATIRadeonX3000GLDriver.bundle/Contents/MacOS/
4) install aty_init if you dont want dvd payer/steam/etc to crash (not for macpro). – http://rghost.ru/20320671
there is still few small glitches (MSAA crashes driver, opencl doesnt work) here and there.
if it stops at gray screen, reset computer, happens sometimes.
Bullet number 4 suggests how to get it working in a Hackintosh.