No actually, the PAIR injects the air in the exhaust ports of the head, well before the O2 down near the cat.
After reading up more on this PAIR and the O2 sensor, i agree with you that it won't screw with the ecu; i recommend this mod to anyone who wants to remove that snap crackle pop; as it will have no negative effect on the fuelling of the motor. The reason for this is that the PAIR pump only operates on deceleration and being slightly lean in that band is inconsequential.