Controller-less WLANs

Does slave Instant AP in the cluster contacts Activate and Aruba Central?

No.  Slave Instant Access points that are part of cluster  would not  initiate a connection with Activate or Aruba Central. It is only the Virtual Controller (or) the Master Access Point that would reach out to management servers like Aruba Central, Airwave and Activate. 

VC would obtain the configuration and then pushes to slave access points.