My advice: don't use IAP, but connect the AP's as campus AP's to a (redundant) Aruba Cloud Services controller.
IAP is a great feature, but if you are talking about that many AP's in conjunction with high density and maybe a lot of roaming clients I would definitely advice a controller-based architecture compared to a controller-less architecture.
I have seen and did a lot of troubleshooting in multiple environments with a controller-less architecture (not only Aruba Networks IAP solution, but also AeroHive) which had different problems. Some problems were related to the switched network, because a lot of roaming in a high-density network has serious impact on your wired network, because MAC address tables need to be updated constantly whenever a client roams to another AP. Furthermore, depending on your VLAN design, you shouldn’t forget to tag the correct VLANs on the switch port to the access point in a controller-less architecture, because all traffic is locally bridged at the AP.
I read the VRD, but experience tells me to advice a controller-based solution in these situations. "A long time" ago I wrote an article about this discussion.