1998 Mitsubishi Galant 2.4 ECM/IM wont reset, have been through 6 drive cycles

Hello, No the cat will not cause additional monitors not to set, and it is not throwing codes because the monitors are not ready to monitor the system. The comparison of the front and rear O2 sensor is a decent way of looking a it, but the rear should not be nearly identical to the front. The catalytic converter should be cleaning up the exhaust. If everything else is looking right, you might just have a mechanical issue, or the data set needs to be compared to the reference ranges in the repair manual to see if those values are indeed within spec. The ECM could be bad as well, but not likely if everything is running tip top. Now, the ECM will run the self-check several times, restarting every time it finds a fault unless a threshold is met. It is designed to get a pass when at all possible. What I'm getting at is that there must be a fault there somewhere, and I would start by inspecting the circuits for the O2 sensor heater, andO2 sensors, followed by testing the EGR valve and solenoid circuit. I wouldn't actually test the cat until I resolved the issue with the heated O2 sensor.