Use tags!  Create the initiator groups for each host, and then tag multiple initiator groups with the same tag.  You can then either right-click on the tag name under initiator groups, select Create/Modify Mappings, and then select the LUNs to map.  Or you can select the LUNs, select Create/Modify Mappings, and then search for the tag name to find the IG's with that tag.
We have the need to isolate select volumes from certain hosts in a cluster.  Specifically, with AIX LVM in a cluster, while we allow HOST-1 and HOST-2 to see the same "shared" volumes (as the same HLU!), we need to insure that HOST-1 does not see HOST-2's boot volume, and vice versa.    We can create cascaded groups in Vmax to do this.  We can create separate Storage Views in Vplex to do this.  Unfortunately we do not have the option to put an initiator name or WWN in multiple initiator groups in XIO.  So far all we have been able to do is create separate initiator groups for each host in the cluster, but this creates a maintenance issue to insure that every host gets the same volumes added, and mapped to the host as the same HLU.  Does anyone have a better solution to this?  Thanks.
Cascaded initiator groups in XtremIO?