US Citizens Working for Foreign Entity

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Our client is the US subsidiary entity of a European company. The US entity is the Plan Sponsor, and the EU entity is not a participating employer. My understanding is that the EU entity + US entity consist of a controlled group or ASG, since the US entity is 100% owned by the EU entity, and the two coordinate on the same business purposes.

They recently informed us that they will be hiring a US citizen who will be working & living in the EU country.

If the person is working for an EU entity that is an non-adopting affiliated employer, do they have to be considered in the coverage testing for the Plan? Additionally, is their foreign income Plan Compensation, even if it's not reported on a W-2? Derrin Watson/ERISApedia seems to say so (Q 20:16 Who's the Employer)