DHCP tells you what was leased. It does not tell you what is answering.
Your DHCP server knows which addresses it assigned. It does not know which of those addresses are answering on the wire right now. That gap shows up in every hybrid network where static devices, reservations, and stale leases sit beside active workloads. Leased and live are different questions. DHCP scopes answer the first. Subnet ping-sweep answers the second. Together they give IPAM fresher last-seen context without handing an NMS credentials across the network.