Whichever Provisioning Server performs the operation will generate the notification and place it under the container named after itself. Each Provisioning Server will only process their own notifications (i.e. pull from the container named after itself).
Identity Manager does not do any load-balancing. Identity Manager has a primary Provisioning Server (any additional Provisioning Servers are failover only). We do not support trying to load-balance the provisioning servers as you can cause race conditions. If Identity Manager is executing Explore/Correlates those will get sent to the primary Provisioning Server and notifications will get generated on that Provisioning Server.