When a (Fibre Channel) multipath disk is discovered by the assisted-installer-agent, the wwn field is not included:

  {
    "bootable": true,
    "by_id": "/dev/disk/by-id/wwn-0xdeadbeef",
    "drive_type": "Multipath",
    "has_uuid": true,
    "holders": "dm-3,dm-5,dm-7",
    "id": "/dev/disk/by-id/wwn-0xdeadbeef",
    "installation_eligibility": {
      "eligible": true,
      "not_eligible_reasons": null
    },
    "name": "dm-2",
    "path": "/dev/dm-2",
    "size_bytes": 549755813888
  }, 

Thus there is no way to match this disk with a wwn: root device hint. Since assisted does not allow installing directly to a fibre channel disk (without multipath) until 4.19 with MGMT-19631, and there is no /dev/disk/by-path/ symlink for a multipath device, this means that when there are multiple multipath disks in the system there is no way to select between them other than by size.

When ghw lists the disks, it fills in the WWN field from the ID_WWN_WITH_EXTENSION or ID_WWN udev values. It's not clear to me how udev is creating the /dev/disk/by-id/ symlink without those fields. There is a separate DM_WWN field (DM = Device Mapper), but I don't see it used in udev rules for whole disks, only for partitions. I don't have access to any hardware so it's impossible to say what the data in /run/udev/data looks like.