We have recently installed IPAM on to the same server that hosts NPM. It was explained to me that they collect different sets of data but work well together. We do not use dns. We have assigned host names to ip addresses and we expected to see all of the host names in IPAM.
So the way that I would expect to see the two tools work together is, we assign an ip address to a host name using the IPAM tool, and I would expect to see the host name and ip address within NPM sitting there as an orphaned host. Then we would assign it to a group in which that subnet is associated with. However, if the node was entered manually through NPM, I would then expect to see that assigned ip address in IPAM and its associated hostname in the proper subnetted network.