The term "DDI" is redundant and superfluous. But it's proven an effective distraction to the market from the true IPAM capabilities, or lack thereof, of certain vendors. You see, IP address management, IPAM, comprises the practice of managing IP address space, from which DNS and DHCP configurations can be derived and deployed. The term "IPAM," initially coined in the 1990's, incorporates IP address management, which itself includes DNS and DHCP configuration.
Why would an IP engineer define an address pool on a DHCP server in a vacuum, independently of the IP address plan? An address pool corresponds to one or more IP addresses on a provisioned subnet which rolls up to an IP address block managed by the IP network manager. Likewise, a device's DNS resource records, especially those referring to a device's IP address(es), namely A, AAAA and PTR, relate to an IP address on a similarly provisioned subnet.
The inter-relationships and dependencies among these three core functions necessitate an integrated approach, not one of loosely associating each major sub-function. The analogy is one of a tire manufacturer who at first simply extends the current tire business model into "wheels." Then seeking the broader more lucrative automobile market, derives the term "tires, wheels and automobiles" or TWA! Why settle for an automobile? Obviously a working automobile includes wheels and tires, though they may be interchanged independently, just as a true IPAM solution includes DHCP and DNS, which also may be interchanged independently among DHCP/DNS reference implementations.
So beware of new and different buzzwords for established practices. It makes for good marketing hype but it probably also masks a major deficiency. I visited my eye doctor today and he said he was in the market for a car; I could have told him not to settle for just an automobile, to make sure he considered the new TWA solutions as well if there was such a thing, but I would have advised him to stick with the tried and true automobile approach instead for a complete integrated solution.