Use of Magic Items
Energy Draining By Undead Or Device (p.119) 
| Energy draining in vanilla AD&D is framed in cosmological terms — a consequence of the alignment-dependent nature of undead. That framing does not apply in Oath-Bound. |
For low undead — reanimated tissue without agency — energy draining is a physical harm event, adjudicated under the non-combat damage model. There is nothing cosmological about it; it is what this kind of thing does.
For high undead, the picture is more complex. An entity that retains agency and exists in fundamental opposition to the covenant model may operate through mechanisms that sit outside normal nwyf interaction. The mechanical effect of energy draining applies; the fictional framing is addressed in the Divine Actor corpus alongside the broader treatment of undead.