Hi all
In case you ever need to do this, the solution for me was to manually edit the igroup setting for the dataset using the ONTAP command line.
igroup set -f dfpm_DATASETNAME ostype vmware
Because the hosts (WWNs) were members of multiple igroups in my case I got an error when I tried this:
os type change conflict found with group
I had to remove the hosts from all igroups except one, then run the igroup set -f change for each igroup, and add the hosts back in. So it may require a host or VM outage depending on your configuration.
Hope this helps.