The good news is that Nearby supports iBeacon in addition to Eddystone beacons.
Using the Proximity Beacon API you can totally register iBeacons and attach data to them.
Then, you can tell Nearby to give you messages for the attachment data associated with these iBeacons (in Nearby, you just specify the attachment namespace for the appropriate strategies):
MessageFilter filter = new MessageFilter.Builder()
.includeNamespacedType("my-attachment-namespace", "")
.build();
Nearby.Messages.subscribe(client, messageListener, Strategy.BLE_ONLY);
See this Stackoverflow question for more hints on how to register an iBeacon using Proximity Beacon.
The note you saw is, however, correct: iBeacon is not supported on Nearby iOS just yet.