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I don't believe there should be air getting into your oil reservoir through the oil cap. The idea of the AOS is to separate gases in your crankcase from the oil and vent them back to your engine to be burned. This reduces emissions and increases power by maintaining your crankcase at a negative pressure. Excessive air coming through the cap, into the case, and into the intake manifold through the AOS, after the MAF, will cause your engine to run with an improper fuel/air mix. This will result in the CEL caused by error codes from the O2 sensors and/or MAF.
This is fairly trivial, and the DME is a little over sensitive to emissions issues.
If the AOS starts to fail then the gas from the crank will entrain oil into the engine causing the engine to smoke. (And ruin O2 sensors, which of course leads to CEL)
If it's air/gas coming out of the oil cap that's bad. Either the AOS is clogged (not real bad), which will produce a slight positive pressure in the crankcase, or you have some serious ring blow by. (bad)
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