I suspect that the reason the devs opted not to set up WMI scanning on IPAM was that WMI is measurably more resource intensive than SNMP. On the NPM/SAM side people are generally willing to make that trade-off for the additional information and convenience that is available, but I imagine someone must have thought at some time in the past that it was a bit too much load for not enough value on the IPAM side. Have you checked if there is a feature request in place for WMI polling in IPAM? If not this is the time to make one to see what the general need looks like.
IPAM does not support WMI during subnet scanning