Is epistemic supervenience a conceptual truth?

This is what is needed in order to avoid Blackburn's critique. But epistemic supervenience has been challenged by Keith Lehrer. Cuneo notes, in a footnote, that if Lehrer is right about epistemic supervenience then the ethical doesn't supervene on the non-ethical either. But I thought supervenience was supposed to be a conceptual truth, in which case Keith Lehrer is making a conceptual error. If we think that he's not making a conceptual error, then we have to ask whether it's a conceptual truth that ethical truths supervene on the non-ethical (as has been assumed).

It's his coherence theory of justification that allows him to ask whether epistemic supervenience is false (let alone a conceptual truth!), and if we think that this would be plausible in ethics maybe that would answer Blackburn's claim that it's a conceptual truth. (But here too we have to be concerned about whether, in a coherence theory of ethical justificaiton the work is being done by ethics or by a coherence theory of justification, in which case we might just be forgetting why ethical supervenience makes sense).

Enoch says that metanormative realism is justified, because it's indispensable to our deliberative project. We simply must deliberate over what to decide--it's non-optional. Am I missing something, or does deliberation need nothing beyond hypothetical imperatives, as opposed to categorical ones? Is his view entirely consistent with a kind of relativism?