My position is that moral truths are not relative, exactly, but agents can of course have different goals. We can know what is Right, as long as we define it as "right according to human morals." Those are an objective (if hard to observe) part of reality. If we built an AI that tries to figure those out, then we get an ethical AI - so I would have a hard time calling them "subjective".

Of course, an AI with limited reasoning capacity might judge wrongly, but then humans do likewise - see e.g. Nazis.

EDIT: Regarding EY writings on the subject, he wrote a whole Metaethics Sequence, much of which is leading up to or directly discussing this exact topic. Unfortunately, I'm having trouble with the filters on this library computer, but it should be listed on the sequences page (link at top right) or in a search for "metaethics sequence".