This articles applies to Aruba Mobility Controllers running ArubaOS version 6.3 or above.
When Airgroup is enabled, controller act as an mDNS proxy. It terminates all mDNS packets received and initiate new query/response mDNS packets.
When the forward mode is tunnel, AP sends all 802.11 data packets over a GRE tunnel to the controller for processing. Therefore mDNS query being a part of data packet would also get terminated on the controller.
The mDNS process on controller will receive all mDNS packets destined to UDP port 5353 with destination IP address 18.104.22.168, irrespective of whether the packet is coming from a wired client or from a wireless client.
Therefore, even though guests clients might offer airplay, airprint and any other mDNS service, they will not discovered that service is disabled in airgroup on a guest vlan.
For example, if vlan 10 is a guest vlan and would like to disable airplay, then screenshots show how to disable a airplay service and how to verify thereafter: