Someone more expert than me on loan regs would have to speak to that. I think there would have to be a balance between the requirement to provide specfic reasons for denial with the expectation that you not 'tip off' the SDN.
(A little silly, I'll grant, since the list is publicly available. In the organizations I've worked, we try to not tell people they're on a government sanction list if we can avoid it. So, I'm only speaking from my own experience.)