1. Can i integrate CPPM with Aruba central? If my Aps are spread across the globe and CPPM is in Data center.
You won't necessarily will be integrating central with ClearPass but you can push the config to the IAPs from Central so that IAPs can communicate with ClearPass .
If the IAPs are able to talk to your ClearPass server in your DC then you shouldn't have any issues.
2. In the same setup (Central with CPPM )can i use AD,guest and on-board and on-guard services?
Same answer as the one above , the Aruba Instant will be the device interacting with ClearPass for (802.1X, Guest , Onboard) and the necessary configuration will be push from Central.
3. If above is supported and if i have 1000 Aruba central APs, how to i am going to add those as radius client in the CPPM server? Or i would need to create AP groups and make one of the AP as Virual controller.
What you can do is enable Dynamic RADIUS proxy (DRP) and that will allow you to use a single IP per IAP cluster as your RADIUS client in ClearPass
http://community.arubanetworks.com/t5/Controller-less-WLANs/What-is-dynamic-radius-proxy-and-related-settings-in/ta-p/180918