The rules for angels having Cover versus the Mortal Mask Numina are a bit unclear. However, I assume that since the DtD core book refers to angels having Cover, that this is the mechanism by which angels who take on human form do so in the material world.
Given that no angel has a Cover rating, does this mean that their Cover is immune to compromise? That there is no investigation, inconsistency or odd behavior that could force a Compromise roll for the angel's cover?