The current transformers should be resonable tolerant to a DC part. With some loads a DC component can happen. A relatively common example are hair dryers on the lower power setting that use a diode to reduce the power to half. AFAIK for hand held use this is allowed in many regions.
I would not expect the CT to saturate under some 100mA, as few materials get saturation under 1 A/m and 10 cm magentic path is still relative small. So it would be hard to make the CT saturate so early. Chances are they would prepare for some DC and intentionally use a material with current needed for saturation / leaving the good range.
None/few of the US meters are designed to tolerate DC, and in my experience you need very little current to saturate, single amps range. For MID metering in europe, they require to be tolerant to a half-wave rectified load of full current rating, and therefore you need to design CTs in weird ways. E.g. you usually have a dual (or even sometimes triple) core CT, where one material is high-permeability for high accuracy for normal loads, and a lower permeability to keep it working in case of 30A DC or whatever, but at slightly degraded accuracy.
Re: even harmonics: for a DC-tolerant CT, I think you're right, they can't measure DC but may be able to measure even harmonics. In general all these edge cases can corrupt, and break:
- RMS measurements of V and I
- Power factor measurements
- Reactive power calculation
- Frequency measurement (e.g. when it's done based on zero-crosses
Does that imply that the active power becomes inaccurate?
No, it does not!
OP, I think you're really confused about how conducted EMI works, and how high-frequency stuff can affect metering. All that 10kHz or 100kHz or whatever, gets attenuated to nothing in the input filters, it simply doesn't meter it.