So my question is thus: do moral philosophers resolve moral questions,
or do they simply help us understand them?
I believe there’s not a definite answer to the question. A philosopher of ethics may only help us to understand a question or problem of ethics, or he/she may argue for a specific position on moral right or wrong.
But I think one major deficiency of modern discourse on ethics as practiced by agnostic/atheist philosophers is a common failure (or fundamental inability) to argue for a universal basis for ethics. I believe that’s a direct consequence of an atheistic/agnostic view of the universe which is void of (or explicitly rejects) a supreme extra-human principle, truth or purpose against which to moderate or regulate human natural selfishness which is a highly problematic issue in all atheist discourses on ethics. This ontological deficit I believe is why atheist philosophers are usually (and in my opinion destined to) get caught up in desperate attempts at bringing human natural tendency to self-interest in line with the kind of self-less decisions that underpin public/collective good. Thus they can at best be expected to only discuss and examine different views on ethics often without an ability to make a final definite judgment.
But, in contrast, philosophers with an ontological/metaphysical approach to ethics are more likely to argue for or against a certain position in an ethical debate. The examples of the latter are theists who argue from presumed divine infallibility of a religion (though they may not necessarily be able to logically reason for their positions especially for a non-believer who doesn’t recognize the authority of scripture); or they may be metaphysicians/theist philosophers who make definite statements on ethical behaviour based on logically reasoned notions of supreme truth(s) or principle(s) that, when adopted with conviction, can be shown to effectively moderate/regulate the human tendency to self-interest as the main theoretical and practical impediment to both ethical theory and conduct.
A prominent example of philosophers with a metaphysical approach to ethics is Plotinus whose ethics is underpinned by his highly compelling theory on the nature evil and goodness, where evil is equated to matter and evil behavior is subsequently traced back to a desire for or attraction to material forms rather than the intellectual forms -- which emanate from the One --, or the One itself which is the first self-caused cause of everything and every goodness. His thoughts are also effectively used by theist scholars to explain religious ethics as his metaphysics substantially conform to the religious worldview. For a summary of Plotinus's philosophy see: http://plato.stanford.edu/entries/plotinus