Originally Posted by ChipsWithDips

Depends on the tuner. The car has both narrowbands (to verify the cat works), and widebands (for fuel control) on each bank. So it is possible to tune based on the stock widebands. Often the dyno has it's own O2 that can be stuck into the tailpipe, or into a spare bung in the exhaust.
The narrowband can also be temporarily removed and the dyno's wideband put in it's place.