To clarify have you already added the hosts initiators to the initiator group ?
You will need to also add each host initiator to a zone config, creating a zone for each initiator and targets that it will communicate with.
Both of the steps above can be automated by use of scripts/API although adding the initiators to the igroup is a pretty simple process.
What type of FC switches are you using ?
You can script this easily from the Nimble CLI. It would be something like this:
for x in vol1 vol2 vol3; do vol --addacl $x --apply_acl_to both --initiatorgrp NewInitiatorGroupName --lun 100; done
Just replace the volume names with the volumes you want to modify and use the correct initiator group and lun values.