Nah. The oxygen sensor is after the manifold and before the cat. So the o2 sensor feeds back info about output after the manifold and therefore whatever goes into the cat, the ecu/o2 sensor doesn't care/monitor.
This is unlike later cars that measure the output coming out of the cat and compare the output prior to and after the cat, and may adjust the mix accordingly.
In my case, changing out the oem cat for a total new exhaust system front to back made b****r all difference.