If there is an O2 sensor BEHIND the cat, it will likely set off a CEL. this can either be turned off via custom tuning OR tricked by a Spark plug anti-fouler.
If not...the computer knows no differently.
Having run a myriad of catted/catless setups on my 4.7 WJ, I would advise you to remove the OEM cat....but weld in a Thunderbolt metallic substrate cat. It's the closest thing you can get to running no cat. I have run and and the difference in sound between it and a catless setup is none. They cost around 55-65 shipped.