The rules and phase outs for Roth IRAs are based on a modified AGIs and specifically reference FEIE excluded income. The rules for 401(k)s seem to be based only on "compensation", and I can't find anything that requires income excluded using the FEIE to be excluded from "compensation" for contributing to a Roth 401(k). For that matter, I can't find anything that distinguishes between traditional 401(k)s and Roth 401(k)s as far as eligibility requirements or allowable compensation rules go.
