One can use a 3200XM as a controller for AP-205s. the 3200XM only supports AOS 6.4
The APs will discover the controller via:
DHCP option 60/43
DNS resolution of aruba-master
ADP - multicast Aruba Discovery Protocol
- hard coding each AP in apboot level with the IP address of the 3200XM.
Perhaps the easiest is to configure the 3200XM as DHCPD for the VLAN where the APs are connected, it will provide it's controller-ip in option 43.
In the 3200XM, we should see log messages and datapath traffic from the APs as they connect.
show ap database
show datapath session | inc <AP IP>
If the AP-205s are operating as controller-based AP, and the 3200XM has a relatively basic configuration, and the network between 3200XM and the APs allows bcast/mcast - i'd expect the ADP to work.
If the AP-205s are currently running IAP software 6.5 and above, they should use UAP discovery, find the controller and try to convert - which AOS 6.4 cannot accommodate, so one might have to outfit the IAPs with AOS controller-based AP software, and then connect them to the 3200XM with AOS 6.4
Reference:
https://blogs.arubanetworks.com/solutions/aruba-unified-ap-platform/
Hope this helps.