1) yes it is; a cel can be triggered for a number of reasons other than a simple increased emissions issue. This could also cause it if you have a first stage tune that is meant for stock midpipes and you go catless or hfc and your tune does not account for that. If your tune is meant for catless of HFC you should get no increased emissions warning triggering a cel - however, i dont see why a cel caused for other reasons would not appear as that is plain unsafe for the engine should something else go wrong.
2) You will likely need a handheld tool to tell you if the car doesnt display the error straight up = it could be a host of things.
Jet Black E92 M3