Could someone please tell me if fitted to a 2008 fatbob rush slipons big sucker air kit and a power commander pc111 do the oxygen sensors have to be eliminated  

absolutely not. The slipons do not impeded Oxygen sensor operations in any way and the PC111 is designed to work with them.
Even if you install a full exhaust system (eg. Vance and Hines) they have lags build in so you can move your oxygen sensors across from your factory exhaust.

Steel Cat,

it depends on which PC3 you get. The green one incorporates 02 sensors. The red one doesnt......but does include O2 eliminators so that you can leave your sensors in place but not functional. The O2 sensors are "eliminated " from the control function, but still exist physically on the bike.

Kind regards

Mick

Thanks for the info

David