One ethical epistemology or class of ethical epistemologies is the humanist, another is the theist. A humanist would say "I will believe what I have to in order to give human beings total fulfillment from their perspective. For instance, make it so there's no pain, just 'gradients of bliss', or whatever it is that makes people happy. Or if humans all want something else, give them that." A theist would say "I will believe what I have to in order to be true to God. I would say 'please God', but what if God doesn't want to be pleased? Everything is for him, pursued as purely and stringently as possible."
Epistemologies seem to need to obey a law: the law of defeaters. Any belief can be defeated (at least in theory). So most humanists do (and all certainly ought to) leave some openness to defeaters to their ethical stance (in this case, whether humanism is really the best), and similarly with theists. What kind of things would be considered valid defeaters? How can you compare one ethical epistemology with another? Is there some way to figure out what value system is objectively correct? If we could do that, we would know which ethical epistemology to follow. But we can't derive that comparing epistemology from an ethical epistemology, if we are trying to know which way is best. So we seem to need some other kind of epistemology, which may be able to decide between them.
On the other hand, we might reason that our ethical stance is some kind of basic belief. It could be a direct perception of truth. But again, somehow there would have to be the possibility of defeaters of that. Otherwise, we might risk selling everything out to something unworthy or unreal, or failing to sell everything out to what really is worthy and real, without having any way to back down from that stance.