Second - I take it you are asking about MIL eliminators/simulators/etc?
As long as everything is working OK (ie - properly working MIL Elims/functional O2 sensors), there should be no check engine light. MIL Elims will keep the check engine light OFF provided everything in the "circuit" is working properly.
Having said that, you should pass the "computer scan" at an inspection. However, if they do a visual inspection underneath the car and you are lacking catalytic converters, you will of course run into some problems...